After more than 10 years on my Bach 6,5 AL, I needed to replace my old mpc 'cause it was too worn out. I've tried this obscure "Denis Wick 5880 Trombone 9BL" and find myself very confortable.
I use it on my '80s Conn 88H and I've gained a more clearer high register, more endurance and no loss on low register.
It's a little bit narrower compared to the Bach mpc I was accustomed to but the V shaped cup keep the warm tone I've always liked.
I feel the backbore is very free blowing, more open than 6,5 AL.
I'm playing this 9BL in combination with "Denis Wick DW6182-L Booster for Trombone" for louder gigs (salsa, open air...) but I feel that the lighter set-up has an easier response.