does anyone have experience with them? They are based somewhere in China and sell Valve Art tubes much less than dealers here in the US. Any comments good or bad are welcomed.

If you buy from the source, the price has to be cheaper.
Do a search at AudioAsylum. I remember the same question asked a few weeks ago but don't know the reply.
I almost bought an amp kit from this guy. Didn't have the cash at the time, but he was MORE than gracious in his approach to my sale, AND REPEATEDLY lowered his price to intice my buy. A fellow asylum member recommended his product to me, and told me that, while build quality of the kit wasn't the highest he'd seen, he said it was more than incredible for the price you are paying and the sound quality you recieve. He also said shipping was relatively prompt, because the guy has to order his stuff straight from the Opera factory, which takes a little while, and he ships from Hong Kong. But, for under a grand for 300B monoblocks, WITH TUBES, you're not taking a gigantic chance. When I got serious about buying, he even offered to pay my shipping. Sounds like a winner to me.
P.S. The asylum member also said that the Valve tubes came in top condition, although they had recieved no burn-in.
Oh, someone just posted a review of their amps and service on audioasylum, in the SET section.