I was a bit suspicious of this housing when I first bought it, but I was shocked to find that it works great.
Since I started using it, my Gopro has sat on shore. I have been looking for a way to ditch my Gopro for a while now, because it is such a pain to get the footage off it for editing (without paying Gopro a subscription forever, and besides I don't like their editing tools), and this looks like the solution.
The housing connects to your phone (iPhone or Android) via Bluetooth to give you an on-screen "mouse". You can then use the 4 navigation buttons on the housing to move the mouse up, down, left or right, and the shutter button to click. Obviously you don't want to do any mouse navigation underwater, so I moved my Camera app icon to the same place as the Camera app's start/stop recording button, and turn my screen lock off while my phone is in the housing. That way, whenever I want to take a video, I just press the shutter button once (wake up phone), a second time (start Camera app) then a third time (start video), and to stop the video I just have to press the same button once. Super easy.
I haven't tested this down to 40m yet, but I have tested it a lot at 10-20m, and it is definitely waterproof. The vacuum pump option for extra sealing is a nice option but I haven't seen the need to use it yet.