I think the mixed reviews of Youxin are explained by the fact that he can't do some of the more complicated work that DAG and Sherry are willing to try. If he knows he can't do something he'll send it back to you instead of trying, which might annoy people if they're impatient. If I'm getting a CLA for a lens or camera, I'll send it to Youxin every time--he's faster and cheaper than the others. If there is something more complicated, involving lens recementing or the electronics of an M7, I'd send it to Sherry, DAG, Van Stelton or Leica.