I own a Maxi Preamp 2 tester and find it easy to use and helpful in using tubes. It’s a big improvement over vintage Hickoks and others, unless you want a lab grade tester so that you can test tubes under the conditions they will meet in your equipment.
It tests Gain, transconductance, and noise. Unlike most vintage testers it has a chart that gives an average new number for gain not transconductance. That’s not a big problem as you can probably estimate what average new transconductance is by testing a few tubes that you know test around average new. I’ve decided that average new transconductance for 12AU7s is 1400. Unlike vintage testers, the results it gives for a particular tube are repeatable. Vintage testers can give a pretty wide range of results if a test is repeated.
It’s a good tester unless you want to get really serious about tube testing. I’m keeping mine.