I use a GoPro 5 black with a dive housing that also has an extender battery. It gives me guaranteed 4 hours of recording time at 1080p 60 fps and GPS on. I am yet to run the cam down flat. In my mind it's a winner combo. Compared to Garmin I can't do the HR overlay, but I am not sure I ever wanted it.
The housing is this:
Oumers Housing Diving Case for GoPro Hero7 Black/ Hero(2018)/ Hero5 Black/ Hero6 with Extended Battery 2300mah & Bracket, Replacement Waterproof Diving Cover/Protective Case 45M Underwater Photography Shooting
www.amazon.ca/dp/B072WNKBG2/ref=cm_sw_r_cp_apa_i_gpvaEbFYHJ8AJ
It shows as unavailable but it comes under couple other brands such as Telesin: TELESIN 2300mAh Convenient Power Battery Backpack Extended Battery Backup Batteries with Waterproof Case Housing for GoPro Hero 6 GoPro Hero 5 Accessories
www.amazon.ca/dp/B0732WZFTX/ref=cm_sw_r_cp_apa_i_ktvaEb27XJBE9
Inexpensive and totally works.
Since it requires removing Gopros battery door to plug in the extender battery it won't work with models that use a non-removable battery.
Also I am not sure it it would work with 7 and 8.
In my mind, this housing is such a value add, if I were to buy a new Gopro, I'd go with whatever model that housing works with even at the expense of new features.
But since 5 black contains all essential features as is (gps, remote compatibility etc) I am happy.
GoPro 5 is a little finicky when it comes to transferring and editing videos. But records reliably, and video quality is nice.
A big +1 for the Fat Gecko mount.