These are Solid State FET devices, so basically you are turning your Tube amp into a solid state amp. Actually make no sense eat all. The reason people buy tube amps is for the, yep you guessed it, tube sound. These types of things have been around a very long tome but never caught on.
Supposedly these are more reliable, and all that. And they are supposed to come out with power tubes as well......
So if I want the reliability of a solid state system. Buy a solid state amp!
BTW I am not arguing the merit of tube vs solid state. But simply why have a tube amp and put solid state preamp and power tubes in it. That makes no sense. Why not go out and get a Axe FX , Kemper, line 6 etc.
BTW many companies make solid state amps with he same circuitry that is in these so call SS tubes. (there is a conflicting statement, solid state tubes)