A great way to exercise when you need "no impact" seated comfort.
I got this in preparation for and mobility after a knee replacement.  It is solid and heavy enough to stay put when you pedal fast, and it works well.  My physical therapist was pleased that I could make use of this between visits to the therapy clinic.  It has many levels of firmness so you can easily build up strength as you progress.  Well worth the cost.
Rating: 5 stars