Intelligent assistants are good at setting alarms.
Other than that, in the real world, they seem to rarely work. You can come up with a curated list and make sure it's all working correctly. But as soon as you do something novel, all bets are off.
Not sure what world you live in but at least on iOS Siri is highly accurate and can interact with enough of the system that it is highly useful.
In the original post's case calling contacts is a trivial exercise and one that works 99% of the time accurately. Reading and sending texts is also a rock solid feature.
Again my main issue with the article was that these assertive features were not even discussed.
And even if you use English, any kind of non-US accent is pretty much doomed.
And even if your accent is 100% Silicon Valley denizen, any app that uses your input for searching will possibly have ambiguities or incorrectness on the results, and currently there are very few tools to correct misunderstanding, even if it doesn't mishear.
And that is assuming that search results are even deterministic, many apps either randomize (or "personalize" for business interests) or update their search logic regularly enough for it to be a problem for a casual user.
Calling a taxi to the wrong destination (for example) is very much not acceptable, ever.
Other than that, in the real world, they seem to rarely work. You can come up with a curated list and make sure it's all working correctly. But as soon as you do something novel, all bets are off.