I have a flycam nano used only for skiing so can give you a little help.
I bought it over a glidecam because of the obvious money saving, but you definitely lose performance. The build quality is not the best. The first one I got could not be balanced properly. Same story with the second so I got a refund without sending it back, I guess the guys on ebay figured it was worth it to save on negative feedback.
Anyway, it was free so can't complain too much.
For use on the hill, it actually does an OK job, even without being balanced 100% it smooths shots considerably with practice. Don't get me wrong, it's far from a professional piece of kit but you're bouncing about a lot when you're following someone through the park so constantly have your free hand on the body of the unit to move the camera and keep it a little more level etc so no stedicam will do 100% of the work for you.
Is it as good as a glidecam - Absolutely not
Is it good for professional use - Absolutely not
Will it piss you off trying to set it up - Probably
Will it make shots of you and your friends look better for a cheap price - Absolutely
I guess it comes down to your cash flow. If it's a choice between glidecam or flycam, glidecam all the way if you can afford it. However, if it's a choice between flycam and nothing (or a monopod). You'll get better shots with flycam than handheld by far.