I've lent it out a little, and got complaints that it doesn't provide enough lumbar support.
For me though - I have upper back/shoulder issues, and this this is GREAT. It's loosened up things that have been bugging me for a long time.
I've over used it the last 2 days (since I got it) and had to stop because it's making my back sore (but we're talking 8ish hours a day usage - not anything close to the recommended 30 minutes/day).
It's definitely helping. I just need to take it slowly. These problems have been going on for years, and I can't expect them to clear up in a couple days.