That having been said, I'm not completely sure that the F cimbasso isn't a better bass trombone than a B-flat slide instrument with the two rotary valves and all of the tubing back by the player's head.
It seems like every time take a bass trombone player's place - whether it's in an orchestral symphony, a big band, or in a brass quintet, the other players' eyebrows raise, and in a good way... and this includes other trombone players.
No, I can't do a seven position or six position or five position glissando (depending on whether one or the other or both rotors are depressed or not), but I can do a pretty good lip fall and I can rip up through several notes (and smear across them as I do so), if and when a glissando is rarely written for the bass trombone.
Admittedly, a whole bunch of the F cimbasso instruments are too big as far as their valve section bore sizes are concerned, and some others that are not too big are - for whatever reasons - are out of tune so severely that they require main tuning slide triggers.
What trombone players don't want to think about is the fact that - for quite a few years and well into the 19th century and a bit into the 20th, depending on who and where - most of the time symphony orchestras first players played E-flat trombones, their second players played B-flat trombones, and their third players played F or G trombones. They were all smaller, but today almost all wind instruments are bigger than almost all wind instruments were back then. Further, those who of us who have looked at pictures of old orchestras and old bands noticed that valve trombones were not uncommon during olden times, so the F bass trombone with valves really isn't illegitimate... it's simply that it's not done, and that's not a particularly strong argument for or against anything in particular.
I don't claim to have based the design of my instrument on anything other than dumb luck, but I have proven that an F cimbasso can be built that's easy to play, easy to play in tune, and can be picked up and (if a remarkably good one) can be played on for only a day or so (ie. reacclimation) prior to using it on a professional job.
Another problem that trombone players have when they see someone covering a bass trombone part with an F cimbasso is that it knocked some trombone player out of a job, and that's probably the most difficult thing for them to deal with. After all, we all need money.
EDIT:
Okay. I'm going to make one more statement that has nothing to do with the title and it's probably even more controversial than the title...
I believe there are more than a few symphonic works whereby a really big bass trombone is a better instrument to play the part than any sort of tuba. I've made it quite clear that I take a lot of liberties with pops arrangements - deciding which ones really belong on the tuba, and which ones feature de facto fourth trombone parts which were assigned to the tuba, because that's the only instrument that covers that fourth chair. I believe that there are more than one or two so-called "serious" music composers who have probably made the same choice, and - if Giuseppe Verdi preferred a more strident sound in the fourth low brass part - other composers probably would have as well, given the choice, and they probably thought that - for all practical purposes - they really didn't have a choice.
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