I regularly play my Holton TR395 Superbone. As a eupher, I can play technical passages with the valved left hand, but when things slow down, get the free blowing effect of the slide in my right hand. Since the valve section consumes some tubing length, the horn actually has a 6 position slide. For 7th position, one has to use 6th plus 2nd valve or valves 1-3 and 2nd position, or 1-2-3, or ....I think of it as my small bore tenor trombone with piston actuated F, G, Eb, A, B, C, etc. attachments
The superbone is a very small bore (under .500) and seems to use trumpet valves. The bell is large (9") and the horn can be very "blatty" when played like Maynard did, using a trumpet or even normal trombone-ish embouchure. However, I find that if I use a 6 1/2AL or 5G, I can get a very nice classical sound out of the horn by using my more relaxed euphonium embouchure to darken the tone. Response is pretty good as long as I stay away from using more than 2 valves at a time. Intonation is suprisingly good. This horn was extremely well made and except for its small bore, is in every sense a professional quality horn. Unfortunatly, Conn-Selmer shut down the Elkhorn, WI factory where Holton made this horn and they are now out of production.
I have enjoyed my horn, and used it when doubling 3rd T-bone parts for pro-gigs. Except for the derisive snorts when the pros first see it, they actually have been impressed by the sound.
Doug