I think http://www.similarsitesearch.com/ is the best search engine for finding similar websites. It's hard to distinguish the differences in search engines for finding similar sites for popular websites like flippa.com. I saw all of them returning the similar results except that similarsitesearch.com gives more results than others. http://www.similarsitesearch.com/ generates the best result for smaller websites like moreofit.com.

BTW I think moreofit.com has very good UI. Better than any other similar ones I have seen.