I have 2 friends who have them. One uses his bike to commute to work and has put a lot of miles on it. He's had a few problems, which I have helped him with. The most significant one was cracks in the rear rim at the spoke holes. Rad Power sent him a complete rear wheel at a discounted price (bike was out of warranty), but it took a while to receive it. He continued to ride it gently during the wait.
The hub motor was a Shengyi brushless direct drive unit. He and I, out of curiosity, disassembled the old hub. It turned out that the drive side bearing was shot, which explained the noise he had been hearing for the last thousand miles. The bearing is cheap and easy to replace once you have the hub apart, but that's the rub ---> in order to take the hub apart you have to de-lace it from the rim, fix it, and then rebuild the wheel. There is no side plate - the spoke flanges are built into the 2 sides of the hub body. This means, that for most people the wheel is a throw-away when bearings go bad. I still have his old hub and am considering hooking it up to a wind turbine. It produces 3 phase AC power so I'd have to add a full bridge rectifier to convert to DC