I haven't use sjcam m20 yet. I have go pro 3 and git2. Best bang for the bucks is git2. Great support and DCT forum is awesome with helpful peers. Eken H8 would be my next experiment when my git2 breaks.
H8 is not true 4k. At least Gitup Git2 is upfront about their specs. 2k is decent for everyday; unless you are making a movie with your action cam. Git2 should satisfy your appetite.