I think "whatever works" are the operative words here. Plenty of people are successful at feeding in separate containers...and if it's working for them, there's nothing wrong with doing it that way. What gets a bit frustrating is the reason that most are given as to why they should feed in a specific feeding box. The whole issue about snakes associating your hand with food if you feed them inside their enclosure is bunk. BUT...if you want to give other reasons...such as reducing the chance to ingest substrate, containing any mess, a smelly box priming the snake to eat, it's what the snake is used to, etc....that's fine and nothing wrong with either method.
What makes it all sound so conflicting is when folks insist (either intentionally or unintentionally) that their way of doing it is the only right way.