The Maxi-Preamp & Maxi-Matcher are very accurate and reliable, absolutely no complaints about them after some years of testing with them. Costly but worth it, if you have many amps and care about what’s going in them.
It’s a personal choice, but it’s one big investment to do and your set for...
If it’s what i think it is. It’s just an external regulating power transformer. To have more steady readings. Depends on the moment of the day, your home voltage may slightly vary and give you different results.
The VFE Merman (Klon type) for very subtle boost. If I want a tubescreamer but something transparent I go with the Cusack Screamer. It retains the main tone of the amp.