This is a very good tube amp.
This version comes with USB-C connector. Connecting to my Win 10 laptop did not require any driver installation and immediately noticed better sound stage and imaging on my DT 990/600 open-back headphones. The high trebles that are known of these headphones are now tamed improving listening pleasure. The included Chinese tube produced these results.
After emailing Xduoo support, I found that USB-C port requires separate power and therefore connecting iPhone with a USB-C to lightning cable will not work and actually did not work for me. Connecting iPhone with a USB3 CCK cable and with separate power might work but someone needs to confirm this.
Before this tube amp arrived, I was using my iPhone with my DT 1770/250 closed-back and the sound was ok. After I received the product, I changed the tube to a Hammond/Mullard and listening through my iPhone (3.5mm to RCA cable) and the sound is really laid back and warm. I will continue on this setup and I have some GE including triple-mica tubes on the way and will try those as well.
This is a very good tube amp in terms of quality of the sound.