I just went to Flygrip's website to view more pics of it and it looks like you're paying for more than just the clip. Down in the lower right of the list of clips, it has "Complimentary cases w/purchase of Flygrip." With the price for the clip being what it is, I don't see the case as being 'complimentary.'
I think the concept is nice, but I don't see it as being very practical except for use as a stand (as one picture shows). I just held my iPhone 3G and noticed that my little finger is across the bottom of the phone and my other three fingers are spread pretty evenly across the back. Having a non-slip case on it, it seems quite stable that way. And with my finger(s) not 'clipped' to the phone, I feel I have a little more maneuverability too. I can set it down, put it in my pocket, or hand it to a friend without having to first detach it from my hand.
One more thing, it adds more thickness to the iPhone or iPad than a non-slip case would.
But the colors are nice!