They're basically bullet-proof from what I've read. I hear they take a few thousand miles just to break in, and last literally forever. Besides, they can be rebuilt if need be. As far as efficiency, I think the top 7 speeds are about the same as a derailleur, the bottom 7 speeds a little less efficient. Overall a great product which I would buy in a heartbeat if I could afford it.
Old thread, but thought I would add this. I've owned some of these for ~10 years now. It's reported by the company that there has never been a failure that has rendered the hub un-rideable.
It excels at mud/etc that would jam a regular cogset/derailleur. It also excels if you want something bulletproof that's almost maintenance free for YEARS at a time.
There is a small efficiency penalty when things are dry/clean. When things get muddy... it's about par for a nasty normal drivetrain. The penalty is a slight sponginess. It's minimized if you have a good clean pedal stroke & cadence.
Yes, it took hundreds of miles before the thing quit sounding like a washing machine. It's dead quiet now.
You can shift while pedaling forward, stopped, or pedaling backwards.
Gear 11 is direct drive.
Here's a shot of it on a my mtn touring bike. It was a retrofit... in a perfect world I would want adjustable dropouts.
Pic of one on my trail riding mtn bike.