All testers can become tools of destruction for tubes with any life left by stripping emissive material from cathodes. Several times I have found a "lazarus" CRT that was literally raised from the dead, but not before I got rough with the HK's more controlled rejuvenation function. The BK 445 shorted a 21ALP4 K-G1 that refused to budge the needle on the HK.
The key is to get a look at the CRT in operation, confirm voltages to it including HV and at the video output tube. And, if it checks out yet looks sick then start slow and follow directions. If there was a brightener attached or you suspect some one has belted the CRT before, stop after doing the cleaning operations or you will strip whatever is left on the cathodes. I had a 21FKP22 (syl) that was fried beyond help.
I have not had success cleaning a Sony trinitron, or most one-gun tubes from the 80s and later. Supposedly the cathode material was not just a coating but the entire element.
The best overall tester is the Beltron due to it's not pegging meters like the Heathkit. But like the HK, cannot adjust G2 voltage, needed for certain tubes.
Beltron close up.jpg
The most versatile tester is the B&K with adjustable G2, though its filament voltage should be monitored. The Color 1 and Color 2 were specified for 21FJP22 and 23EGP22 respectively but both will run the heater in this 25XP22 at over 7.6 volts
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25XP22.jpg