I've been using a hero 3+ for a little bit now. I use it for everything from bowhunting to rooster hunting to fishing. They work great with only a couple downsides, battery life is shit. If you continuously record expect about 25-30 minutes of battery life if you get a WIFI capable unit and actually use the WIFI. Also, like others have stated, Audio quality is not very good if you use the waterproof case. I'll link some of the accessories that I use regualarly.
1.
https://www.amazon.com/gp/product/B014UTMZ5O/?tag=nodakangler10-20 This is an excellent mount for gun hunting. It clamps right on to the barrel of your rifle/shotgun and does not harm the barrel. It is very secure.
2.
https://www.amazon.com/gp/product/B00RMNBNRW/?tag=nodakangler10-20 I've only used this one 1 time. seems pretty neat, but i got it late in the season last year and didn't really mess around with it.
3.
https://www.amazon.com/gp/product/B00MPFLWEQ/?tag=nodakangler10-20 This is the mount i use the most as it use it for bow hunting. It works awesome whether your in a tree or in a ground blind.
One thing that I would recommend if you buy a go pro is this, buy extra battteries, and a portable charging block like the one on this page.
https://www.amazon.com/gp/product/B00FSA361M/?tag=nodakangler10-20. And then go buy one of those portable power packs for like $40 at best buy or walmart. Thats what i use in my blind to keep my batteries charged up. Works well and is pretty compact.
Also, another thing to do is make sure you get the gopro app on your phone and link the phone and gopro up. Even if you don't use the app to control your phone, have it linked up just in case because there's an awesome feature built into the app that if you should happen to lose your gopro while out in the field, you open up the app, turn on the "find Gopro" feature, and then your gopro will start beeping allowing you to find it. One of my buddies lost his brand new gopro last year the first time he used it while we were out chasing roosters in a bunch of cattails... Never did find his gopro because he didn't have it linked to his phone.