I just feed mine reg rats,I don't think it really matters that much...
I have one who just made the switch to rat pups with no problem,he wants nothing to do with FT only live,and will only eat if put the prey in the tank and turn the day lights off and night black light on,then in about out 10 mins he comes out and does his thing.
but I'd say just stick with reg rats. There easier to get,supply plenty of fat ,calcium and protein,unless your breeding your own asfs,you can just be asking for a headache down the road...this is just my opinion.