I recently played 6 different Kanstul models in various keys. Last year I got a chance to play Bob Carpenter's personal 5490 CC. I thought it played very well but there was some ergonomic issues. The main body of the horn would press against your stomach (I don't have a huge belly), and the placement of the valve slides were not in the best of locations. Since then, Bob Carpenter and Tom Treece have worked very hard at solving those issues because of the frequency of those same complaints. The result is a great horn. In comparison to the 90, which I played last week, the 5490 is much more free bowing top to bottom, MUCH better intonation, low range is much freer and easily accessible, ergonomically better (I'm 6'2"), and is closer to that one of a kind York & Sons sound. I give it 2 thumbs up!!
Hope this helps.
Jeff
The United States Army Band, "Pershing's Own"
PT-6S
MW2250
I played one a few years ago at TMEA and it's low G ( 4th valve below the staff ) sucked. That is the litmus test for me. If the low G sucks, I'm out. And on that particular horn, it sucked.
Kanstul labels the 5490, a fairly substantial instrument, a "5/4" tuba. Does that imply that they have (or plan to have) a 6/4 size scale design CC and/or BBb?
I heard that the problem with the 6/4 was the tooling for the bells -- they would need to build the tooling first, and then they can start making the tubas.