Salt fog, I was thinking same thing.
I like my larger bore snorkel, Only problem I had with it was reflecting in my eyes off the bottom of snorkel, some black rubber tape fixed that many years ago.
That snorkel would not work for side roll clearing.
The ABS fitting, just seemed like wrong material for mouth comfort. Could make a simple mold and cast something out rubber.
No Orange flagging on the end so divers and boaters might spot you. guess it depends where you are in water.
It might work in future , it does need some more R/D effort. Those mono fins sure are spendy.
Why didn't he use that vice for all the sanding/grinding?
A 1 inch belt sander would be good equipment upgrade for him, I love mine, you get those Zirconia Alumina belts for it and it grinds stainless for a long time. a 42" x 1" belt is around $2 each or less on Enco. The Kalamazoo Belt Sander, Model 505-1371 for $286 is a great tool.
Food for thought to you guys with mini shops in garage.