Years ago, I was sent this (mailed to Texas - as Mrs. bloke and I were enroute, where my son-in-law formerly lived) the day before a shared recital with him at UT Arlington.
(At that time, he was principal horn in Fort Worth.)
I plugged it in, and it played PRECISELY like my non-skeletonized (identical INTERIOR dimensions) mouthpiece that I had been using.
I thought it was a hoot, so I used on our at-his-house one-time run-though, at the university for the one-time run-though with Steven Harlos (AMAZING pianist) and on the recital. It was the SAME as my other mouthpiece...NO difference (other than looks).
Oh yeah: The RIM was ALSO skeletonized.
The "skeletonized" rim design was kept, and is what is produced to this day.
Those of you who bought some of my very early mouthpieces (and then later bought others) surely noticed the difference.
Mouthpieces are thick chunks (even when skeltonized) of brass, steel, Lexan, bronze, or what-have-you. They are not conducive to vibrating, and a reasonably smooth interior finish will send the player's vibration into-and-through the instrument the same way, if the interior shape is the same.
OK...plastic rims (and more-easily-scratched silver/gold-plated mouthpieces - once scuffed...even by light beard stubble - are more "grippy" than rims which are far more scratch resistant (steel, titanium, etc.) and that contact difference can affect flexibility, but that's about it ASSUMING everything else (rim contour and all interior dimensions) are the SAME.
TRUMPET players' instruments are small and can weigh at little as 2 lbs., so - when they play on a skeletonized OR bulked-up mouthpiece, they will likely FEEL the difference in WEIGHT, whereby they might easily confuse the tactile with the sonic (as so often happens with musicians from beginners to accomplished professionals).
I'm not going to argue with anyone about this. (again: Argue with your spouse or you significant-other...That's what they're there for.) People disagree with each other on things far more obvious that this.
IMPORTANT detail from above which (I tend to suspect) many will tend to overlook:
The rim contours and ALL interior shapes must be identical for two mouthpieces to play the same, but an oz. or two of more-or-less material...nope, no difference.
OK...Perhaps I'm just insensitive.

