I like the group workout with an instructor - makes me feel like I have to keep up with the group and not cheat or quit too early. Pushes me.
The one thing I don't like is how you can't float classes from one month to the next if you don't use all your sessions. I travel a lot for work, and it's hard for me to find OTF in all my rural travels.
Other than that - the workout is awesome, the instructors are motivating and do an excellent job and the staff is always eager to help and welcoming. The app is awesome too and makes signing up for classes a breeze.