Read the stickyI have owned several of Xin's amps, he designs and builds great sounding gear for sure.
Something more important than sound or build quality that I have learned in HiFi over the years is the following:
If you cannot obtain the service associated with the hardware, it makes a difference in the overall total cost of ownership.
Designing a great product is one thing, not being able to fulfill that product and/or service once orders are paid for is an entirely different prospect altogether.
I know that companies like Dr Xin and similar specialize in a boutique environment and a niche market, and that HiFi providers/supporters are accustomed to this nature somewhat. This does not mean that the lines of communication cannot be up kept, timelines reasonably honored, and orders fulfilled accordingly. Too many "loans" are outstanding to Dr Xin for me to feel good about supporting any more of his products personally.