It realy depends on your style to what you will get out of it. As you can see from this page so far; you have some people who say its useful, and others who say its useless.

My personal ipinion is that it helps. It helped me get back into a better rythm for gaging where my muscle fatigue was when I first started spin class, and where I could confortably keep it by the end. If anything it was a workout I was not going to be able to get because of inclimate weather.

Take it for what its worth. Try a few, if you like it stay with it, if not, don't.