I had a Zesto Leto Preamp. I sent it to George for new tube sockets and the ESP upgrade while it was there . I bought it as a demo and believe someone whacked a tube laterally, damaging a socket.
I can't say enough about my experience with George and Carolyn. They are some of the nicest people you will encounter in HiFi. They could have gouged me like many companies would on a product with a $7500 price tag but parts and labor was only around $300 for the repairs. The ESP upgrade was reasonable too and worthwhile.
That was a phenomenal product with great support. Only sold it to fund a DHT pre to compliment my amp. If I could have funded that and kept the Zesto I would have.. it was the most quiet preamp I have ever owned or had first hand experience with. Complete black background