I'm the last person who is going to pull out a tuner and tell you how many cents flat or sharp something is. And certainly not going to rattle off intonation tendencies of the nth partial...
For me, it's pretty simple to hear what's in/out of tune, and then adjust what you can to make it better, if needed. I'm not a slide puller, so I use alternate fingerings or lip things up/down. I've tried some really awful tubas before... Big struggle to play in tune. This 20J is NOT that. It's not perfect, but frankly, I think that's as much me 1) being really out of playing shape and 2) being used to playing a very different rotary tuba. Give this the right air, and there's no issue that I can't deal with. It's just fine!
The harder things for me than intonation are 1) control when playing softly (24" bell in front of my face... That seems like a tough thing to achieve until I get in shape again) and 2) clean articulations (again, the front bell is not my friend, as every bit of everything is hugely amplified and directed. Not at all used to that.
My old Bach 18 megatone from college works really well on this, as it did on my Conn sousaphone in college. But the Thein that I play on my Alex sounds even better... Likely because I've used that mouthpiece nearly exclusively for the last several years, and it's what I know best. It's the rare case, where the mouthpiece cost more than the tuba, so that makes me a little nervous.
@donn , why do you think they sold so many of these? School band programs? They are TANKS and take a beating and just keep going. But ouch, I'm a grown man and this thing is no fun to carry. It's far heavier than I think it will be... But it's also not as huge to hold as I think it will be.
My son always wants to play it, so I sit the bow on the floor and hold it up, and he walks up to it to play. Works well since he can reach the valves and blow at the same time... And for 5 years old, he's pretty good at it!
Ramble ramble ramble... Was fun to play the tuba this weekend.