I've got a Hero 3 Black. They are awesome little cameras. I bought mine mainly for taking pics of fishing trips. The wide angle lens is great for closeup shots, but stinks for anything out there. If you're gonna use it for hunting and mount it to the Tree your in or on your weapon, don't expect to get great video out past 20y.
I have a hero 4 white, that is currently in Washington county at Jesse's. Mine has WiFi, which allows it to be used with a remote if you buy one for $50 lol. You can also download the videos straight to your phone with the wifi. Animals must be 30 yards or less to get any good video with a gopro. I got mine on sale at Walmart for $200.
If you get one, turn of the red blinking LED light which shows it's filming... A deer will bust you in a heartbeat when it sees you... Also, there's a view finder option, don't use it in low light shooting either as it lights your face up while filming....
They are nice for close range but as far as a 20-25 yard + shot, you will not be able to see much detail as far as impacts.
J and I both have the mounting bracket for a gun or fishing pole.
I have considered using it mounted on a "gorilla arm" hung from a tree closer to the shooting lane and using the hand held remote to turn it on before shooting. I may also suggest getting some canned footage before of you I'm the stand or nest watching and swinging up to take the shot for editing later.
GoPro has a decient free download for editing that's fairly easy to use for putting it all together once it's all done.
If you're looking at one, check Walmart right now if you don't mind having an older model. They have last year's cameras on clearance and accessories as well. I scored these three accessories for $41 today. Retail is $160.