> not to mention you're asking them to code a (potentially) complex take home project, that could take over an hour, for free.
An hour, I'm fine with. It's less than what I'd schedule for an interview, and far less than I'd schedule for an in person interview (which might include a flight out). On the other side of it, though, I'd be concerned about cheating. It wouldn't be too hard to hire someone to take the test for me, I'd imagine.
I had a friend of mine who told me her company doesn't use online programming tests (like hacker rank) because she doesn't think legit programmers would bother with positions that required them.
Having taken a couple of these on-line automated tests, I don't think I'd take them again. Problems which I'm sure I had written correctly, dealing for edge cases and testing in browser; I submit to get like a 6%. Programming simple things in front of people in an interview I do fine.