I've had this stepper for nearly 4 months now, and I love it. I have had no problems with malfunctions, aside from some squeaking that WD-40 fixes right up. It's easy to use, and easy to store away when not in use.
I'm in the process of losing 100+ lbs, I'm down 80 so far. When I first got the stepper, I was only able to use it for 10 minutes before I felt like I was going to die. In a good way. I worked my way up to an hour and a half, and it's a great way to burn calories and get a sweat on. I now use it just about every day as a warm up before the rest of my workout. I was worried about it eventually not being an adequate work out as I became more fit, but I don't see that happening any time soon.
I expect to use this stepper until the day it dies, and I'll probably buy a new one when it does. I already feel I got my money's worth from it. I recommended it to a friend who wants to lose weight, and she loves it, too.
Update 4/27/2018: I've lost my hundred pounds, and I still love this stepper.