Portable Exercise Bike

I found this bike pedal portable thing about Carol Wright Gifts few years ago, but was not willing to pay ten dollars plus shipping if it was crap. I found in a thrift store one day. I love it and it feels like I'm riding a bike in first gear. I was wondering if this is a good way to exercise without having to buy expensive and space consumption stationary bike. A link to the latter is also provided

Thank you for any response.

http://www.carolwrightgifts.com/cwg_v2/c ...

Once, I wanted to get one of those and put in my computer. I do not know if it will not slide up and down and sideways as it is used. but only $ 10, what can you lose?