I have the gopro hero6. A $400 investment. While I am completely aware the gopro itself is now waterproof (with correctly closed housing doors up to 10m), I like to go deeper than 10m sometimes, and when I don't, I tend to put my camera through pretty "water-violent" situations. In other words, under big waves, tossing up in the air into water, accidentally running into some reef or coral every now and then, etc. Simply put, I put my gopro through a variety of situations that can easily lead to 1) my lens getting cracked by a drop on a rock 2) housing doors becoming unlatched by accident underwater 3) any situation that can scratch/damage the camera or jeopardize its built-in waterproofing.
If you're like me and want peace of mind as well as GUARANTEED SAFETY OF YOUR $400 INVESTMENT, this $50 will give you both of those. I never, I repeat NEVER, go underwater without this housing. Even though I know my gopro will be totally fine in a swimming pool, I never take the chance and suit it up before getting anywhere near the water. Do I need to you remind you the gopro is $400??? This housing is not just waterpoof to much lower depths (for you snorkelers/scuba divers out there), but it also protects against drops, scratches, lens cracks.
Additionally, salt water is a lot more abrasive and leads to higher chance of damage than pool or fresh water.
I dont just recommend this to anyone with a gopro hero 5 or 6, I am TELLING you to just buy it and you'll thank yourself and me later. Regardless of how you use your gopro, buy this housing. It is a must. $50 pales in comparison to having to buy a new gopro.