I've got a Go Pro and it's pretty useless for most hunting applications. Waterfowl and bowhunting it's pretty good but anything over 50-60 yards is gonna be out of range for the most part. I'm going to sit down and make a scope mounted cell phone bracket one of these days. A couple people make them but I'm not paying $50+ for one.
I've got the hero 4 black, it does pretty good at those distances. Im not aware of anything small enough to be mounted that has optical zoom. Unless that new camera, ion, is equipped with it.