I was about ready to post that it looked like a scam from the complaints I saw by searching... but then I ran across their Amazon.com page.
They've got literally thousands of positive reviews, and almost all of the recent ones are glowing. But if you dig back into the history, you see that a few months after they started up in 2008 they were getting something like 5-10% bad reviews. Some sound exactly like the complaints that you can find elsewhere on the 'Net - "Never arrived", "Had to file claim for reimbursement", etc - and the seller often posts comments in response that are incredibly defensive and blame either the customer or the shipper.
I don't know what to think. My gut feeling on it is that someone got fired for not doing their job (then trying to hide the evidence or blame someone else), and after that it was smooth sailing.
It's your call, but if it were me I'd be willing to place an order.
(Disclaimer: For clarity's sake, this is just my personal opinion. I'm speaking only for myself; I'm absolutely not speaking on behalf of Kumoricon or as a moderator.)