First I've heard of them (but I'm not any kind of expert). Are they good? I usually just hear the usual suspects mentioned such as iXSystems and Supermicro. Linux guys will mention one called PogoLinux every once in a while also
I have bought a few servers from them (4 or so over the years), and they have served me pretty well so far. I haven't had to do any RMA's or replacements though, so not sure how good the company is about that.