We bought this for a number of varied uses, and most recently used it on a rugged 1 week wilderness canoe trip, including whitewater rapids for our GoPro 6. The build quality was great and it sealed well and held up to a lot of abuse, while protecting the camera from soaking, dunking and banging around. The lens was clear so there were no optically issues, and we were still able to hear and record audio. We took the go pro diving and again there were no issues with the case at all. It is quite expensive for what you get, however, I purchased a few other generic cases and none have held up or were as optically clear as this.
The biggest challenge was having to remove the lens from the camera in order to put the GoPro into the housing, but that's a GoPro design issue they need to address. Our concern was losing the lens cover when we took it off to put into the housing. My earlier versions of the housing (4) fit over the lens and didn't suffer any optical issues.