I dunno - my ck would take food from my hand. Guess it depends on each fish. I vote for a clown knife, though one may grow fast enough so that it might try eat your clown loaches depending on their size.
There is a risk with flag tails, I'm not saying every one will suck on bichirs but look in the gar and bichir sub forum and you will see quite a few incidences with them harassing fish with ganoid scales.