I wonder if the unit has a
valve signal path. I mean that, like if the unit ONLY has a tube make-up gain or something else. So far I can see is, that with just the 3 tubes on the output gain, the actually valve effect is minimal compared with a real tube compressor/EQ unit. Even with a vari-mu compressor the tube changes I heard were not staggering different, or like others the output tubes were, the ECC88/6922/6DJ8 or whatever sort output tube, are selected to built in that period anyway.
For me I wouldn't buy like the mentioned
"Best" sounding output tube. You pay good dollar for them and you need 3 pieces. The effect what I had with tube changes are like a subtle lower noise floor, higher gain, with a possible boost/cut in the frequency at minimal level difference with the stock tubes in comparison. But that's just it. Nothing spectacular compared to the current tube outboard units around the same, or yes, for a bit more, price offerings made today.
That's me. Yo!