Ask HN: Experience with co-founder search sites?

Looks like there is no shortage of startups that attempt to match potential co-founders. From a quick search I came across names such as startupwithme, cofounderslab, founderdating and matchfounders but I'm sure there are more. Has anyone used any of these? Do they work (for some definition of "work") in general? Any specific anecdotes, positive or negative, you can share?