there are 2 things in a bt - the fee, charged once at the time of the transfer, and the apr which is different from the purchase apr usually.
there used to be some cards with 0% FEES on BTs, in addition/instead of apr offers, nowadays i dont think those are around. theyll all charge 3% ish. the only thing to worry about or look for is the leignth of the promo apr.
i hope i understood all the back and forth in this discussion...