Nothing is perfect, but this really is the best feature ever in IOS 10 for the 6s and above. One less physical button to press. This is a great button saver and a quicker way to turn on the screen.
Like anything else, takes a while to get used to. Occasionally, it does not come on as intended due to the angle it was raised but I've learned to quickly placed it back in the horizontal position and raise it up to the vertical position and it just works. Easy!
It does turn on in my front pocket if standing up from a sitting position. That's like 3 seconds of screen on-time times the number of sitting/standing motions a day while it's in my pocket. So if I average that motion (while it is in my pocket) say 100 times a day, that's only 300 seconds or 5 minutes wasted screen-on time a day. Hardly a noticeable hit on battery life, unless one it obsessed about battery life.