I'm a huge tube fan, have multiple amps in that realm, with 100s of tubes =O
I used to be SS only, (even had Carbon + 009), but slowly transitioned away from all that.
Anyway, I needed a beater amp, I found it used for $1450 couldn't pass that up.
I previously had the loaner, so I wasn't completely in the dark. I'm not great at reviews, so I'll give my own interpenetration in simple words.
Why did I buy this since it's technically SS (hybrid)? Well it doesn't sound like tubes, it does sound like an SS amp, BUT...
Although it's more similar to an SS sound signature than tubes, the nutubes fix enough of the SS annoyances I generally have. For me, all my SS amps have a bit of grain, glare. The nutubes take that edge off, without sacrifices detail or exactness.
It's what I would consider the battle between tubes musical liquid sound v.s. SS sterile exacting sound. The Sangaku fits inbetween those tonal signatures, making it a great general purpose amp (imo).