Never heard of them either, but I must say the templates are clear and rather nice. Of course, your websites would need to be in the raneg of quite common topics. I wonder how they do for content when it comes to much more specific subjects. Unless there is some kind of autofeed, there will be limitations very soon. Moreover, the issue of duplicate content (raised often in other threads) might become extremely acute if hundreds or thousands of customers rely on the same content, unless they completely renew their content on a very frequent basis and don't sell the same to hundreds of customers.
If you want a website of your own and are willing to invest a little bit more per website, PPC-Sites could be a good idea - duplicate content, true, but probably much more diversified.
I see however a market for somebody who would be willing to provide custom minisites, just a few pages, but avoiding more or less duplicate content. Maybe there are actually already some people doing it, just I don't know them. Would probably need to be people outside of the West, if they want to offer such content at competitive rates (e.g. slightly above PPC-Sites, but within similar price range.