I re-read the original questions. Are you also thinking of taking pictures (not videos) underwater with your Gopro? IMO, get a compact cam. I honestly have never seen a good underwater photo taken with a gopro, wide angle or macro. Hence to me it is a waste of time. With a gopro, stick to videos me thinks.
by the way, if you want to see what a gopro+macrolens can do, check out my video at
Note that this was my first attempt at gopro macro hence it was not very good. But i think that there is much more room for improvement. I took those videos with a selfie stick in one hand and a video torch in the other hand. Not exactly the best technique haha. Next chance i get, i will try 2 video torches, a stable base and double stacking my macro lens. Hope to get better results.