The guys who do this for a living pretty much to the man use a regular scuba tank, itching fancy. Consider that you might be over thinking this.
Or given the silly device mentioned, under thinking this.
My history is technical mixed gas diving and many many hundreds of dives. Personally I hate working on my own boat underwater and hire someone. When I do an inspection or clearing a line in the prop resulting from mine own stupidity, most often I use a snorkel. At least once I had to borrow a pair of shorts from a guy twice my size and tie them on with a dock line. There are a number of folks here who have great luck with an inexpensive oil less compressor, a long hose and a second stage. But honestly, if you canít make a snorkel work, just grab a scuba tank. Keep it simple. My boat rig was nothing but a harness and a single tank. You really donít need much.