i've got the 5k, i like it's looks.
i'm happy with the quality of video and it's run time/waterproofness etc.
the negatives are
heavy on helmet mount, no way to point up or down using the mount.
No chest mount (i think this would offer the best position)
Undamped bar mount so footage is extremely shakey on anything but smooth trails.
Stands quite proud of the mount, so limits fitment and causes potential head strikes.
No lanyard attachment in case of knockage.
Sounds like i'm being pretty negative, it's a great camera but i think it could be better – if i could go back in time i'd buy a go pro with chest mount.