Been using the HS 81s sense time began without problems at both 4.8 and 6 volt for a number of controls. They do react very fast compared to other servos at the same voltage but other then that I haven't seen anything odd. The motors are very small so I tell most people to use them for nothing in a standard glow or gas type plane besides throttle. I have used them on the ailerons of small over powered race planes in the ailerons without problems a couple of times but it's not something I do on a regular basis.
The gear train is nylon too, just something to give thought to. Today we have servos in the same size with metal gears, I will be using them in a scratch build I'm doing right now for the small ailerons. I'm not sure about the trust issue but I use them and have used them for years without a failure. That could just be a lot of luck on my part?