No, they are hard too get out of the way. When I used one, I found it nice at times, but I quickly found that it wasn't right 100% of the time, and it was in the way of attempts to use a chair. If it was convenient to switch between treadmill and other modes I'd probably be 20% treadmill, 20% kneeling, 50% standing, 10% sitting in a chair. Since I've never had all options easily available I'm only guessing.

I have used them in the past. You need a very slow speed. Even a normal slow walk is too fast - you are trying to think about something else while your feet move, if you want to exercise that is a different thing.