I have had the GoPro Hero 3 plus Black Edition since October 2013 and it has been used on almost a weekly basis along side my Hero 3 Black Edition.
As thought the form factor of the actual camera remains the same. The Hero 3 will fit in the GoPro Hero 3 plus case and vice versa. Visibly there is little difference between the cameras, although you can tell that the lens is different. This translates to what I can perceive as a very marginal improvement in the quality of the images/video being taken.
The biggest physical change is in the case. It is much smaller with a lower profile clasp, and although this feels secure it is a pain to try and release. I like the secure aspect of the design but I do not like trying to open the case up. The previous version on the Hero 3 is much easier to open.
The changes in the case make the whole unit much lighter. The lens area is much smaller and is fastened to the case from the inside rather than from the exterior. This means that changing the panel will be possible if it were to get scratched or damaged in any other way.
The difference in weight between the Hero 3+ and the Hero 3 case is noticeable. This is especially so when the unit is worn on my kayak helmet (Sweet Strutter).
All of the bacpacs that I own (LCD and Battery) fit the camera without issue. This is great but it comes with some bad news mixed in for good measure. The doors used on the Hero 3+ and Hero 3 cases are of a different size. Having spent a small fortune on Hero3 backpacs, I am glad I am able to use them on the 3+. I contacted GoPro with the issue and they apologised and sent a Hero 3 case through to me. A nice gesture but not an ideal solution. It seems at the time they did not have accessories with backdoors that would fit the newer slimline case.
The choice of SD card is even more important than on the Hero 3, especially if shooting on the most high resolution settings. My thoughts on suitable SD cards can be found – right here.
On that issue I haven’t really used the camera to its full potential. I do not have the kit capable of viewing 4k quality HD I have not tried to use these settings and have firmly stuck with 1080p. If you are in the same situation I would suspect that the Hero 3 Black Edition may be a good option unless you manage to find one of the many bargain Hero 3+ sales that seem to be popping up and an ever increasing rate.