I am biased, but I didn't like a few things about active admin:
1. Customizing views requires that you use Arbre. Learning an entirely new tool for generating webpages when every developer is already familiar with partials, html, erb, etc seemed backwards to me.
2. I tried to design upmin-admin so it was easier to setup. Active admin requires a little bit more work (but truthfully not a ton more).
3. Adding things like actions was significantly easier in upmin-admin. You basically just say what method you want to have on an admin page and it makes it work.
That said, this is very early stage (beta at best) and active admin has been under development for a while, so active admin is definitely more polished right now. That should change over time.
Definitely +1 for for using default Rails view system. I've been fighting Arbre every step of the way every time I try to do something a little out of the ordinary.
The view handling in Active Admin has always been a huge problem for me personally. I find myself at home with most any other Rails gem, but when it comes to Active Admin I always shudder and think "now I have to remember how to do things the way Active Admin likes them." Often I'll end up burning half an hour trying to figure out how to implement functionality that would normally take 5 minutes just because I have to figure out the Active Admin way. Anything that gets back to standard Rails action/template generation (like Devise) would be a godsend in the admin area.
Re the choice of haml - you don't have to use haml. That just happens to be what I chose to use, but if you watch the videos you will see that you can create partials with erb files instead.
I intentionally used erb in the videos to try to get this point across, but perhaps I should try to make it more obvious.
Just a quick glitch-in-the-matrix report... in your video about using your own widgets, the state of the shipment was "out for delivery" or something like that. But when you added the widget and refreshed, it showed as a few states behind.
1. Customizing views requires that you use Arbre. Learning an entirely new tool for generating webpages when every developer is already familiar with partials, html, erb, etc seemed backwards to me.
2. I tried to design upmin-admin so it was easier to setup. Active admin requires a little bit more work (but truthfully not a ton more).
3. Adding things like actions was significantly easier in upmin-admin. You basically just say what method you want to have on an admin page and it makes it work.
That said, this is very early stage (beta at best) and active admin has been under development for a while, so active admin is definitely more polished right now. That should change over time.