Can you use a single natural weapon for all attacks during a flurry of blows with feral combat training or can you just use the natural attack in place of one unarmed/monk weapon attack?
Lady J is incorrect. FCT lets you use a natural attack as your weapon for the flurry. Nothing lets you flurry and then pull of a natural attack that I know of.
No, turning into an octopus to get free grapples and constricts on your flurry attacks, a bit T-rex with 1 awesome bite attack, or if you get free trip attempts on hits or whatnot.
Yes, this isn't a always good feat. but a niche good feat.