B & K Model 666/606 Dyna-Jet Tube Tester

[Captainclock]

Hello Everyone today I was given by a friend of mine from church a B & K Model 666/606 Dyna-Jet Tube Tester and he said it didn't seem to be working right the last time he tried it out (which he didn't tell me when that was) and considering that so far he had given me to work on for him an old SuperBeta Betamax machine and an old Yamaha Natural Sound Stereo Receiver both from at least the mid to late 1980s and they both worked perfectly for me without much work needing to be done to them I'm guessing that the tube tester will be the same way and that maybe he just had a really wonky tube he was testing because he said that the needle on the tester's dial would go up and then it would move around back and forth a lot (which if the tube was extremely leaky or gassy it might cause the needle to move around a lot and not give a stable reading.) We'll see I guess.
What do all of you think of this tube tester? Is it any good or is it just a piece of junk?
I've always heard on here that B & K tube testers are pretty decent machines.
Picture is posted below of said machine.

Oh and it came with all of its original manuals including the setup booklet.