Don't like it.
Came with my quanum trifecta and did not fit very well. HK recomends this servo for the trifecta but the gears from trifecta yaw mechanism do not fit properly on this servo. There was a lot of play.
I am wating for it to break and replace it with something better. But after some modifications with ducttape around the gears I was able to reduce play between the gears of servo and yaw mechanism to a minimum. And suprisingly after - 40 Lipos flown and crashing with Trifecta the servo still lives.
I had a similar problem with my Trifecta: When I installed the servo, the servo lead didn't fit in the tail boom and the servo chamber wouldn't close completely, causing the gears to slip in crashes. I used a hobby knife to remove some material from the frame where the lead comes out of the servo, and now it closes completely and the gears never slip anymore. 10 flights and a few crashes later, the servo is going strong with no further problems.
Update: Finally managed to strip the plastic gear on a very aggressive backward crash. Had another 9018MG on hand, swapped them out and the Trifecta is back in the air. Given the circumstances of the failure, I'm inclined to think that the plastic gear serves as a fuse, an engineered point of failure to protect other components in horrific instances of pilot error in which one or more beers may have been involved. If I could buy a ten-pack of that gear, I think this servo would last forever.
This servo is ****. Bought two with the Trifecta frame. Didn't even make it through one battery before the plastic gear in these "metal gear" servos stripped. Opened an RMA case with HK. Almost 3 weeks later my case is still "waiting initial evaluation." I uploaded pictures and video of the stripped gears. In the meantime, I replaced with a Corona 929MG servo. Perfect fit, works great, and seems to be quite durable based on the aggressive flying and crashing.