i'd been waiting for these to come out (for men); and just got a pair yesterday. they are destabilizing, so they require more effort to stay upright. the first 30 minute session was more effective than expected. my lower abs were definitely working. that said, my legs didnt seem to be getting much out of it. anyway, they make a great addition to a treadmill desk, because they provide another method to make walking more difficult. so now i can throw on a weight vest while wearing the shape ups, and still keep the treadmill at low enough speeds to accurately use the mouse and keyboard.
i'm not sure if i would wear these to the gym on leg day. wearing these shoes while trying to do squats might be a bad idea.