exactly one of the reasons I suggest EVERYONE with tubes should get a basic tester.
Basic confidence from a basic tester takes you out of the dark, that’s all I’m saying.
Test new purchases, of course! Annual testing, of course. Some problem, find or verify it is or is not the tubes, then work up the line until source of problem is found. No tester, how the bejesus can you have confidence in your tubes?
Happily when I have bought matched sets, they have measured matched, and I KNOW that, not HOPE it’s true. You would have been in a mess without your tester, as you say, it saved you!
My past comparisons of my big tester to my little one gives me the convenience of using the small lightweight one, easily transported to a friend’s home to test their tubes.