Backscatter's Airlock was my decision for a pressure test device for my housing. It came this week and I've installed it.
1. Completely mechanical. No batteries to go dead or electronics to fail.
2. Footprint is small and adjustable (direction). Clearly would fit in the available real estate.
1. More expensive than the Vivid, which was the primary competitor in my decision.
2. Competely mechanical, no ability to check pressure at any time.
It was easy on the Aquatica housing. Remove a nut on a blank bulkhead. Insert the furnished fitting and tighten a nut. I don't know why it bothered me to open a hole in the housing, I open a bigger one everytime I install the Aquaview viewfinder before diving. And now and can test my work for both.
The manual pump easily reached the recommended -5 inches of mercury for a pressure test and the -10 inches for locking all ports in place. The pressure did hold overnight. And since there are no electronics or other items to evaluate it's done.
I am removing the valve for packing the housing, closing the bulkhead fitting with the included cap. Packing pressure on the valve could possibly leverage into breaking the plastic bulkhead fitting. Reintalling the valve will just take a few seconds.