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stick to sharp rims. I played on a helleberg for some time, and then switched to an MF3, which has a rounded rim. The difference sort of shocked my embochure and it took me a couple weeks to get used to the rounded rim.

congrats on the R&S i use one, great MP

It ain't broke - don't fix it. I forgot who said something like, "Everytime I think about buying a new mouthpiece, I go and practice three hours on the one I have."

Try find out what suits you , years ago I swore by vincent bach until I chipped the mouthpiece by dropping it , went back to a wick 2xl and tried different types Yamaha ( too shallow) , other bachs ( too sharp rim) , I was recomended perantucci by Les Neish one of the UK's finest young tuba stars and top bloke. tried a few and found the mouthpiece to be very comfy , adaptable for use with different instruments ( my PT36 is brilliant for playing low register stuff on Bb And solo work and high work on Eb. would like to compare with a MF or G&W , I will try the new denis wick helleberg type MouthPiece, to see what they are like , heard good reports from Players who use them already.
just work on what you have .if you need a change always ask your dealer what you need to work on am sure they will be able to advise and let you try a few different Mp's