Yes I have MaxiPreamp II, a MaxiMatcher II and a large collection of tubes. Note you’ll need an optional adapter for 6SN7 and another for 6DJ8 / 6922. It’s very effective for matching (its namesake) but also you’ll learn how to sort out weak versus strong tubes of each type. And of course, toss anything with badly mismatched triodes. I find that modern Russian small tubes (12AX7, 6SN7) when brand new tend to measure higher transconductance than the strongest vintage tubes (even "NOS") by 15 - 20% or so. But then most vintage tubes are pretty consistently good / strong enough (the duds will really stick out) which indicates to me they REALLY last. You’ll learn to grade each category on a curve. When you get a preamp tube that measures bad on this tester, you can HEAR this in your amp (it sounds bad too).
And the MaxiMatcher is absolutely fine with KT120. I had some used sets of KT120 which measured much stronger than I’d expected. I should have kept more of my used sets around before the shortage :(
Over the years I’ve bought many tubes from various private sellers online (here, AA, ebay), and sometimes would just put them away for a while (before I had this tester). Always bought tubes advertised as "tested, strong". Going through my stash, most of these tubes were indeed as advertised, but SOME are real pieces of crap that belong in the trash. Definitely some less scrupulous sellers out there.