Agreed. I know there are at least 2 other members who haven't chimed in yet (maybe you could PM them, search thru threads for circlarc posts and PM the members that haven't posted here yet? ) and there may be more.
I would also agree I'd want some sort of guarantee of a decent lifespan w/ replacement if it failed abnormally early (like say under 100 hours or something) if I'm spending several hundred dollars I want to be able to actually use the fixture daily without fear of the tubes failing in a short time.
I want to wait a bit also because there are other members who have circlarc fixtures and may can help get the quantities up. If so, you can count me in for six. I only want to be guaranteed they are high quality and have a decent lifespan. It would suck to spend that much money on something that blows filaments or leaks vacuum in a short time.