My brother is now wanting a SM4U now that hes gotten alot better at euphonium and he needs a new mouthpiece besides my schilke 51d. He likes my 4AL, but he wonders how the SM4U compares. Is the SM4U essentially the same depth and rim but with a different mass distribution? Or is the SM4U a little deeper? How are they alike and different? He wants a VERY thorough answer and I just don't have a SM4U to see for myself.