I bought a second-hand Hero3+ Black and had a lot of trouble with it. Even after buying the recommended micro SD card and completely resetting / updating the device it would still turn it's self off and then freeze. I do think I was unlucky and got a bad one but I sent it back for a refund and then ordered a Xiaomi Yi which so far hasn't given me any problems at all. Without a doubt the video quality of the Gopro is better but for a £50 saving and a new product instead of second-hand one, I feel I've got about 85-90% of the image quality, which can be improved further in post. (the Yi even takes higher resolution stills than the Hero3+ Black)
Anyway, getting to the question... The Hero3+ Black fitted perfectly in my H3-3D whereas I've had to do a cheeky custom jobbie on the Xiaomi Yi which involved strapping on a few coins to get the gimbal nicely balanced again, and a cable-tie to keep it on. Hopefully I'm not killing my gimbal in doing so because it's obviously not ideal, but I've heard it's the balance which is more important than the additional weight.