In my experience, yes. As with All Things Tuba, however, your mileage may vary.
I have both the R&S models, the TUHH which I believe is based on the Conn Helleberg design, and the TUHH-II which is based on the Schilke Helleberg. The TUHH-II has a smaller throat and a slightly shallower cup than the TUHH (I don't have exact dimensions) though the rim inside diameters appear to be the same. The Clements Ensemble splits the difference between the two R&S models. I haven't seen the Clements Orchestra model.
When I use them on the Sonora, all three produce a darker, more-powerful sound than a standard type of mouthpiece with similar dimensions (such as the Canadian Brass Arnold Jacobs model) will. With the TUHH, however, it's too easy to overblow the Sonora- but not the 20J, so I use the TUHH with that. The Ensemble will just barely start to distort if I give it everything I have. The TUHH-II isn't quite as powerful as the Ensemble, but works nicely with my small Besson. All have similar rim diameters, so it's easy for me to go from one to another.
The Bach MegaTone works as described, when compared to Bach's standard models. I have a standard Bach 7 (dating back to the pre-Internet days when standard Bach was all we could get) and a 7 MegaTone, so I've experienced that difference. I've found that for me, the Helleberg-type rim works better than the Bach-type, but again, someone else might prefer the Bach-type or something else.
Then there's this one, which has the biggest throat I've ever seen. Haven't worked with it much:
http://iymcorp.com/tubamouthpiece.html" target="_blank" target="_blank" target="_blank
There are many others I haven't tried- for example, if I find myself in the Memphis area I'll certainly look in on bloke and see if he'll let me try some of his.
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Many players and teachers will say that a person's technique is more important than the mouthpiece they're using. They're right, of course. But I can compare a mouthpiece to a pair of shoes: If your shoes don't fit properly, you'll be able to walk, but you'll have trouble running. JMHO.