The thought behind a "feeding container" is that if you feed a snake in its cage it will always expect food when you open it and go into "feeding mode", ready to bite and eat. So when you feed you move the snake into another container and it eats there. This way it doesn't try to rush for food when you open its cage. It sort of makes sense to me but I've never done it. The snakes that have the big feeding reactions in my house are the big snakes. I'm not going to carry a 12' snake into the bathroom and feed it in the tub, then tote it back to the cage. Some people swear by it; you may want to try, and if it works for you, follow the practice.
You mentioned feeding pre-killed? That I definitely recommend. Even better is frozen thawed. Why is it better? I pay less than half as much for frozen rodents than for live. When I buy frozen mice I get nice sized adults, live ones I get small adults. Hmm, pay less, get more, that sounds good, right? Ever been bitten by a mouse? They have decent teeth. They can take out a snake's eye, punch a hole in it that can lead to infection, etc. Someone is sure to tell you that snakes eat live in the wild, it's their nature to eat live. You're feeding a snake in a cage, it isn't in the wild. There are other benefits to feeding frozen thawed, if you can't do that at least feed pre-killed.
