Got one on my work/hack bike.
On the whole i like it, but have also had issues with it rotating under load. I'd intended to turn up some different axle ends for it, but haven't gotten around to it yet, so it vacant be that much of an issue.
Mines the original type with std threaded sprocket thread & lock ring.
I think it's a good solution. I had a bike that I liked, wanted a fixed. Seemed like a good solution and a saved an old bike from the scrap pile.