Exercise Equipment - Compact cardio machines

http://ecx.images-amazon.com/images/I/51c%2BA6T6tyL._SL500_AA280_.jpg

Has anyone tried these? Amazon sells several elliptical-like machines that are just the bottom (no hand poles) and also as steppers or bike pedals.

I am interested to know if anyone has something like this. I have no room to put a full size machine in my house and want something to keep me moving while I read or watch TV. An added bonus is that they are like $90 or less. Please fill me in on the good, the bad and the ugly. Thanks!!!!

I'm not sure about them but I have heard that ellipticals with short strides can aggravate knees. I imagine any compact 'elliptical' would have a short stride and thus might be an issue.

I have heard other people say rebounders have worked well for them. Although they aren't exactly small, they can be put away fairly easily.

I have the Tony little rock n roll stepper and I like it a lot. It burns after a few minutes. I've never been able to do longer than 5 minutes but I think I get bored. Although I do miss the walking forward motion when I use it since it's like side motion more