I switched to the TEK about three months ago after maybe six or seven years with the Kinesis (although without the foot pedals). Here's what I would say so far.
1. The TEK feels better in terms of physical key presses. Both use the same Cherry MX Brown switches, but because the Kinesis is a big hollow piece of flimsy plastic and the TEK a very solid brick, the overall effect is noticeably nicer to my fingers at least.
2. The function keys are much better on the TEK.
3. The arrow keys and brackets are better positioned by miles on the TEK. You can remap the keys of course, but the Kinesis only has one column to the right of the 'P' key, it's nearly impossible to find a good place to put them, and I just left them where they are. Similarly, the tilde/backquote key is also on that horrible bottom row on the Kinesis. And those arrow keys...putting left and right on the left hand and up and down on the right hand is one of those things that probably seemed like a good idea on paper, but after maybe seven years using the keyboard, those arrows were every single bit as completely unusable as they were the first day I sat down with it.
4. In contrast, the thumb well ends up being a better place for things like the enter and backspace keys than a single column in the middle, so score one for the Kinesis there.
5. The 209 International TEK has plenty of modifier keys. You get control on each hand, meta on each hand, and a blank key on each hand you can choose how to map. Plus you get a menu key in the middle column, and the space bar is split, so you can remap whichever side you don't use for space for something else. On the Kinesis, the thumb wells only have two modifier keys per side, so if you want symmetric layouts, you're stuck without a command or control key on the Mac, or super/hyper/windows on Windows or Linux. You can remap Caps Lock for that purpose of course, but there's no place on the right hand to put an equivalent key. If you use Emacs on a Mac, you know how badly you need Control, Command, and Option keys, and not having that ability on my Kinesis was one of the biggest reasons I wanted to try the TEK.
6. Remapping keys on the TEK is ridiculously difficult. You have to do the remapping on their web site in a (fairly nice, actually) little Javascript GUI. That part works well enough, but then to apply the changes, you have to download and flash new a new firmware image, which can only be done in Windows. Not in a virtual machine, but with the keyboard plugged into the back of a real USB port on a real Windows computer. I don't own a Windows machine, so any time I want to try out a new remapping, I have to haul my keyboard to work and reboot my Linux box there into Windows. On the Kinesis, you remap on the fly by pressing keys right on the keyboard.
7. I've bought two of both models now, and both are sort of a mixed bag. I can't stress enough how cheaply the Kinesis is made. Every once in a while, I have to take apart the flimsy plastic case and glue the USB hub back down (and yes, it's just glued right to the plastic shell). The TEK is built like a brick, but one of the two has taken a full month of use so far, and it's still not completely "broken in". That's the term that Truly Ergonomic use to refer to the property of your keyboard registering the keys you press. Out of the box, about 15-20 keys either didn't work at all, or else pressing them once would insert anywhere from zero to five or six of whatever letter you pressed. They tell you that you might need to press each key a few hundred times to "break them in". In my case, maybe 25,000 times is more like it. If I didn't live in Iceland, I would have demanded a replacement, but since shipping is such an enormous hassle, I decided to see if it got better, and it mostly has. My first TEK worked perfectly, but this second one still has maybe a 2-3% error rate, either duplicating or ignoring keypresses. Which is way better than the 57% error rate I measured on the 'B' key during the first few days I had it (and several others were nearly as bad).
8. The Kinesis has a USB hub. It snaps away from the case and dangles loose inside the hollow shell occasionally, but you can take the thing apart with a handful of screws and glue it back down at least. The TEK doesn't have USB ports. Not a huge deal I know, but it means that I need a separate USB hub with the TEK, and with the Kinesis, I could do without one.
Summing everything together, #4 is a really big point in favor of the Kinesis. You can get used to either one, but you really have to reach to hit that middle column on the TEK, whereas the Kinesis puts all those keys right under your thumbs. The remapping solution for the TEK is frankly embarrassing, but once you settle on a layout, it's not something you need to do very often. In contrast, the TEK feels better and on the whole, has a layout that is better designed for programmers I think, with the brackets and some other non-special keys in more standard locations. And for me, the modifier key situation is at least as big of an advantage for the TEK as the thumb well is for the Kinesis.
I honestly can't say for sure yet which I prefer. I'm sticking with the TEK for now, and I think, if push comes to shove, that the modifier keys are going to be the clincher, but both are really good keyboards.
1. The TEK feels better in terms of physical key presses. Both use the same Cherry MX Brown switches, but because the Kinesis is a big hollow piece of flimsy plastic and the TEK a very solid brick, the overall effect is noticeably nicer to my fingers at least.
2. The function keys are much better on the TEK.
3. The arrow keys and brackets are better positioned by miles on the TEK. You can remap the keys of course, but the Kinesis only has one column to the right of the 'P' key, it's nearly impossible to find a good place to put them, and I just left them where they are. Similarly, the tilde/backquote key is also on that horrible bottom row on the Kinesis. And those arrow keys...putting left and right on the left hand and up and down on the right hand is one of those things that probably seemed like a good idea on paper, but after maybe seven years using the keyboard, those arrows were every single bit as completely unusable as they were the first day I sat down with it.
4. In contrast, the thumb well ends up being a better place for things like the enter and backspace keys than a single column in the middle, so score one for the Kinesis there.
5. The 209 International TEK has plenty of modifier keys. You get control on each hand, meta on each hand, and a blank key on each hand you can choose how to map. Plus you get a menu key in the middle column, and the space bar is split, so you can remap whichever side you don't use for space for something else. On the Kinesis, the thumb wells only have two modifier keys per side, so if you want symmetric layouts, you're stuck without a command or control key on the Mac, or super/hyper/windows on Windows or Linux. You can remap Caps Lock for that purpose of course, but there's no place on the right hand to put an equivalent key. If you use Emacs on a Mac, you know how badly you need Control, Command, and Option keys, and not having that ability on my Kinesis was one of the biggest reasons I wanted to try the TEK.
6. Remapping keys on the TEK is ridiculously difficult. You have to do the remapping on their web site in a (fairly nice, actually) little Javascript GUI. That part works well enough, but then to apply the changes, you have to download and flash new a new firmware image, which can only be done in Windows. Not in a virtual machine, but with the keyboard plugged into the back of a real USB port on a real Windows computer. I don't own a Windows machine, so any time I want to try out a new remapping, I have to haul my keyboard to work and reboot my Linux box there into Windows. On the Kinesis, you remap on the fly by pressing keys right on the keyboard.
7. I've bought two of both models now, and both are sort of a mixed bag. I can't stress enough how cheaply the Kinesis is made. Every once in a while, I have to take apart the flimsy plastic case and glue the USB hub back down (and yes, it's just glued right to the plastic shell). The TEK is built like a brick, but one of the two has taken a full month of use so far, and it's still not completely "broken in". That's the term that Truly Ergonomic use to refer to the property of your keyboard registering the keys you press. Out of the box, about 15-20 keys either didn't work at all, or else pressing them once would insert anywhere from zero to five or six of whatever letter you pressed. They tell you that you might need to press each key a few hundred times to "break them in". In my case, maybe 25,000 times is more like it. If I didn't live in Iceland, I would have demanded a replacement, but since shipping is such an enormous hassle, I decided to see if it got better, and it mostly has. My first TEK worked perfectly, but this second one still has maybe a 2-3% error rate, either duplicating or ignoring keypresses. Which is way better than the 57% error rate I measured on the 'B' key during the first few days I had it (and several others were nearly as bad).
8. The Kinesis has a USB hub. It snaps away from the case and dangles loose inside the hollow shell occasionally, but you can take the thing apart with a handful of screws and glue it back down at least. The TEK doesn't have USB ports. Not a huge deal I know, but it means that I need a separate USB hub with the TEK, and with the Kinesis, I could do without one.
Summing everything together, #4 is a really big point in favor of the Kinesis. You can get used to either one, but you really have to reach to hit that middle column on the TEK, whereas the Kinesis puts all those keys right under your thumbs. The remapping solution for the TEK is frankly embarrassing, but once you settle on a layout, it's not something you need to do very often. In contrast, the TEK feels better and on the whole, has a layout that is better designed for programmers I think, with the brackets and some other non-special keys in more standard locations. And for me, the modifier key situation is at least as big of an advantage for the TEK as the thumb well is for the Kinesis.
I honestly can't say for sure yet which I prefer. I'm sticking with the TEK for now, and I think, if push comes to shove, that the modifier keys are going to be the clincher, but both are really good keyboards.