These spindles are really designed for woodworking applications, and may not last long if cutting steel. I do know of one person who only cuts aluminum on his router and swears by them.
Most people buy them directly from China through Ebay. There are a large number of users on CNC Zone using them, but most use the 2.2KW version, as it has a larger ER20 collet. A small percentage of people have had trouble with them, but it seems that most work great. BUying from Keling will make it easier to return a bad one, but you'll pay more up front.
Also, most people recommend buying a good brand VFD, like a Hitachi, rather than the Chinese ones that typically come with those spindles. The Chinese VFD's are not very good quality.