Other then putting the ball pythons off by moving them to a new container, it doesnt really matter whether you feed inside or outside the cage. Heres why....
There is no "good" reason to feed them outside the cage.
Feeding outside the cage is actually much much more dangerous for you then feeding inside the cage. This is amplified when we are talking about large constrictors such as burmese and reticulated pythons. Moving a large hungry constrictor to a feeding container, allowing it to eat, and then moving it back all with your big hot meat hunks is a super super bad idea and a good way to end up in the ER from bite lacerations.
That said, ball pythons are puny and dont inflict much damage but still all the same risks are taken for getting bit by removing them from the enclosure.