What's a good Tube Tester to purchase?

[old_coot88]

Originally Posted by Phil Nelson

...Certain tube functions (notably, oscillation) can't be tested reliably by a tester. Also, in a surprising number of cases, a so-called "weak" tube will perform just as well as a brand-new one. Testers are useful, but don't get the idea they will tell you everything about every tube in every possible application.

Just my $0.02.

An old service adage:
The best tube tester is the equipment it's used in.
A tube tester is most useful in an auxillary, confirmatory role. Or for a 'go/no-go' weeding of large batches of tubes.