Whatever you choose with those deep pockets of yours, stick with brass. Don't fall for titanium (with those claims of tolerating upwards of ~40% O2); or, for that matter, for a sales pitch that I once overheard, years ago,, dealing with some exotic first stage, said to have been constructed, in part, no joke, of the same "space age" ceramic that produced the tiles on the space shuttle.
Yeah, those did a bang-up job . . .
That said, I've been diving commercially for decades, with Poseidon products; and own the lion's share of the models. They've been bulletproof, from freezing waters to the tropics; have no directionality (no upside-down -- can be used either left or right); breathe absolutely dry; and the exhaust remains off to the side, so there are no streams of bubbles in the face -- of some importance to photographers . . .