I have a big fancy Hickock, and the earlier Accurate Instrument 157.
The little portable 157 has never been wrong. I'd like to have this 257.
I highly recommend everyone with tube equipment to get a simple tester. You live with Tube Confidence!
I check: what I buy; what I am using periodically; what I pull from stock from all the tubes I have been given/acquired.
Used tubes: many tubes last 10,000 hours. I had a friend who gave me bags and bags of used tubes pulled from TV's, etc on the way to the dump. I had a client bring me a gigantic Samsonite suitcase full of tubes he had in his mother's basement, from Chicago to NYC. People's parents die, they give me their father's tube collection. I see a bargain at a yard sale. Point is, the great majority of them are good. Without a tester, you would have no idea.
I just had Audio Classics overhaul my mx110z tube tuner/preamp. I had filled it with vintage tubes (17) I tested on my 'toy' 157. You would expect them to sell me some new tubes. Nope: Ryan said, "they all tested good on their tester, you can't beat those vintage tubes". It came back with new gold-plated rca jacks, what a wonderful thing.