I had one, didn't use it much. Too many distractions at home to try and exercise there and I just wouldn't think about using it most of them. The most exercise I got out of it was moving it from one room to the next, trying to find the perfect location for it where I would remember to get on it.
The one thing that was nice about it was our little boy was able to use it, supervised of course. Since he controlled how fast it went, he was able to get on it and burn some of that energy he had overflowing from his little body.
We've since sold it in a yard sale to an older man who thought it would be safer for him to use too.
Again, it worked great (it was a Jane Fonda version), I just prefer to get out of the house to walk. When I'm at home I get a phone call, a kid who wants a toy off the top shelf of the closet, laundry that needs to go in the dryer, the dishes need loaded, on and on.