Dave,
I am a Kelly mouthpiece dealer.
I talked to Jim Kelly on the phone last night ... they are so busy he is working many hours!
These mouthpieces are copies of Mt Vernon Bach mouthpieces (and in some cases other mouthpieces, for example they sell a cornet 4B mouthpiece which is a copy of a Dennis Wick).
Right now you can get a trumpet mouthpiece in 1 1/2C, 3C, 5C and 7C in all 18 colors. They are working on a 14a4a as the next trumpet piece I believe.
These mouthpieces never get hot or cold. They are great for outdoor playing. They are also great for all around playing. Both french horn players in our community band play them full time. Tuba players LOVE them because they are not cold. Brass tuba mouthpieces can stay cold even when being played. Several trumpet players play them either as a primary piece or as a backup piece. I know quite a few who prefer them for the cornet. They are very comfortable and easy on the chops, so lots of players use them for long gigs.
Mike Vax recorded his recent live album using a Kelly mouthpiece
They are inexpensive and fun. The clear ones can be used to check embouchures. I played a glow-in-the-dark one at Christmas this year when we played outside in the dark. Not only didn't I have to worry about a cold mouthpiece, it was great fun.
I sell the trumpet mouthpieces for around $20 shipping included. For that price, you can have one or two in fun colors. At Christmas, red and green are fun!
Anyway, I hope that answered your question. They are well made and easy to play. A great value too. And they are not a fad. They are selling them at a brisk pace to all levels of players. They only make them in popular sizes, so the closest one to the Warburton would be the 3C.
M&C