Yes I know ............

[Scubee]

OK... confession of a scubee diver

I have done 54.1 on air on a single 15l with a 3l sideslung pony. we went down, had a look, took a couple of pics, then came up the wall. Dive time was 47 minutes.

Would I do it again? In the same conditions (warm clear blue water) and the same buddy (or one at least as good) Probably.
But it wouldn't be my dive of choice. I have learned a lot since then and I think i have become a grown up

[Janos]

IMHO by far the most sensible choice is to use a rebreather for that sort of depth.

However, if informed adults want to choose riskier options, then let them. Treat adults as adults say I.

Janos

[access]

That was a standard dive for me at one time and the pony cylinder only came along later.
A nice 5.5l ex-fire service strapped to the side of the 15l ooh the dives that opened up;
followed by a set of twin 12l’s and then I could go anywhere
Would I do it now? Not a chance