They can tell you if a tube is good... but so will the Orange amps tester too. Which is newer and more reliable.
If you have a large collection of tube amps (which some of us do
) and time is money to you... it’s an easier decision. Wait til you have to repair one of those Hickok or similar testers. The repair bill will make you think twice. And very few people will even work on them anymore to begin with. YMMV.