Light wheels make a big difference when climbing and these are some of the lightest. But what about your reward for all that climbing? The high speed descent... These wheels are stable and quiet at high speed and they have a huge braking surface. I have used these wheels for RAMROD, High Pass Challenge, Copper Triangle, Triple Bypass and several trips up to Timberline Lodge (your basic epic mountain rides) and these wheels quickly transfer power on the way up and on the way down. And when I have hit the inevitable mountain road pot holes, these wheels remain true. In fact I've gotten several years of use on these wheels without ever having them trued. Great wheels.
Incredibly comfortable. Solved my ulnar nerve compression problems. I've heard a few people don't like being fixed at one wrist angle, but for me it keeps everything just right, and greatly enlarges the palm contact area. Not too heavy either. Caveats (1) I do road and XC so I can't speak to downhillers, and (2) unlike the GP3s I ran previously (but took off bc I didn't like the barends), the clamp on these crimped my thinwall XC carbon bars (despite Ergon's FAQ saying the non-barend GP1 is ok for carbon and despite using a torque wrench set at 5nm as indicated).
I bought these wheels to compliment a rain bikecommuter (Soma Double Cross Disc). These wheels are bombproof, reasonably stiff, and for the price you can't shake a stick at them.
I really like how solid these wheels feel on rough pavement. They're not light but they ride like a lively brick ****house. Seriously, for the money, you can't beat these wheels.
I also appreciate that they're completely rebuildable.