Apparently, the promise of a very flexible/robust little tube rolling platform amp, not missing audiophile sound quality regardless of compatible tube used, is true.
This makes it ideal for perfectionist tunners, but opens the range of possible alternatives too wide: I started with a short list of possible output tube candidates (aside from the two-fold driver choices), and it keeps increasing (and this is only on family types, never mind particular brands, build dates or construction ... )

It's good to have choices, though.