As soon as I post this everybody's going to think that I view my stuff as very special, just too amazing for most people to appreciate, and that I view myself as some "unappreciated genius talent in mouthpiece design".
I don't view myself - nor my stuff - in any of those ways, but what I have noticed is that mouthpieces - which are heavily promoted - sell and that there are flash fads in mouthpieces (and everything else, for that matter). I don't have the energy to stand behind tables for two or three days in a row at tuba shindigs all over the nation and around the world, I don't have the interest in running ads in the T.I.U.T.B.E.A.A. Journal, it's just not my nature to suck up to people and glad hand people, nor put on a mask and pretend to agree with all the academic crowd's non-music-related views.
My stuff is stuff that I like and some other people like it.
For a whole bunch of people, there's the "Bach 18 of the college crowd", the XT-50.

(I bought one, tried it out, and sold it after a couple of weeks. I just don't like them at all.) If I didn't have the stuff that people have helped me develop, I'd probably take a Conn Helleberg 120, round down the inner edge of the rim somewhat, turn down the outer edge of the rim a millimeter or so, and just use that. Otherwise, they're not wonderful, but they're not terrible.
Regardless of the cup shape and depth (which affect the sonority...but obviously not as much as a tuba or certainly the player does) I find that a whole bunch of tuba mouthpieces feature rims that are too wide, with interior turns from the rim into the cup which are too sharp, throat diameters that are too large, and claims about materials from which they are made (as well as how much material is left on the exterior) which are nonsensical. I also really like stainless steel rims, because - unlike soft metal rims plated with other soft metals - they stay smooth (you know: like against my skin for hours and hours, day-in, year-out) for a long long time and don't scratch very easily.
I'm not claiming not to wrong about some things and I'm sure I'm silly about others (such as being a skeptic, and still not being sure about believing something even if I see it - or that humans shouldn't be herded into categories or groups, and should be viewed as individuals), but I'm certainly not alone in these characteristics.
Y'all buy 'em if y'all like 'em.
If you buy them new from me, I can buy more soy burger patties, off brand chicken bologna, 10 lb bags of chicken thigh quarters, dollar store cans of French cut green beans, and manager specials at Kroger (yes, really).