Questions on KT150 tubes

Does anybody here have experience using that tube? Can you tell me how it sounds? I have a Primaluna DiaLogue Premium HP and it can use them but they aren't cheap. I'm running the stock EL34s and LOVE it but seems like this tube is all the rage. The Primaluna is unbelievable for its tube magic as-is. Also I wonder if the KT150 would last.

Also the best places to buy them. Not the cheapest. The best quality.