The response times seem okay.
They've been around six years thus far (or the domain has anyway), and the domain is registered until 2009.
They run webppliance as their control panel - I'm unfarmilar about that.
My only worry is their pricing, it does seem cheap. Try and find some current clients and see what they think, directly from them.
I sent them a support question - response was fast (good), and they said this:
</edit>All our server loads are bellow 1. We don't add more then 150 clients per server.