With all the hand-work involved in making those things, he'd have to charge a huge amount of money for each one. Unless there isn't a mass-produced Chinese or Russian equivalent, I can't see how he could succeed.

Then again, some of the more fringe audiophiles will spend absurd amounts of money for things they imagine makes their equipment sound better. It's possible that they could be fooled into thinking that hand made tubes were the new gold standard when it comes to audio reproduction. Might work with guitarists as well.