Well, this is a new one. I am guessing that it is not actually black… as that would hold heat in. I’ll definitely keep track of the product to see if it repeatedly seen to not effect tube life. That would be my main concern. I must have nearly 50 tubes in use among my three systems. (Wow, how did that happen… it was gradual… but once momentum got started… the results in sound reinforced more tubes… and here I am)
The idea behind the product seems valid.