I've been using the "rough" prototype of this new model with (ok: "in my opinion") great success (at least, "great satisfaction") with BOTH my 6/4 contrabass and my 4/4 contrabass tubas. The cleaned up production prototype (pictured just below) exceeds what I've been enjoying with my own rough prototype.

This is the blurb that I posted on other places on the web:
You are looking at the
Sellmansberger Orchestra Grand Ultimate production prototype.
It's similar to the original Orchestra Grand interior shape but with a few tweaks, and with a modified #2 profile (narrow fall-away shape, with 32.9mm embouchure opening) rim.
In silver plated brass, the limited production first run mouthpieces will be priced just as were the first runs of other models of one-piece Sellmansberger silver plated brass mouthpieces at $150 + postage (whereas subsequent runs will be priced at $195 ea.)
The first run versions will be offered in standard shank.
In particular, those who have used something like a model 50 mouthpiece with a contrabass tuba, we would respectfully encourage those players to consider this as an alternative.

tubaforum friends...
Three of the first small batch are already spoken for (as of this posting at the close of 2-25-25). I have given myself until Friday (2-28-25) to increase the quantity of the first production run, but - by then - all of the first production run absolutely need to be fabricated, polished, packed, labeled, and mailed for silver plating.
I should have them plated, back here, and ready to ship out by the middle of March (for receipt in purchasers' homes' mailboxes) by middle-of-March + typical-number-of-mailing-days-from-western-Tennessee.