I really feel like c/c is a sketchy move for Hero, since the board is so scary, what will bet here instead of just checking back, besides the flush?

I think c/f turns this hand into complete spew.

Therefore, I'm left with b/c, which seems donk-tarded, or b/f.

So I went with b/f because there is some chance to get paid off by worse, but mostly I want to get a small blocker bet out there, to protect from the shove vs. most of Villain's range. I said it's a bluff because Hero does not have the flush, which is what a bet reps here.

A $3 bet is about 1/3 pot and just under 1/2 Villain's remaining stack, so it seems like a great amount to force a difficult situation on Villain.