What is the difference between a pocket nappy and an all-in-2?

your description matches my understanding. pockets you put the booster in back, AI2 the boosters lie in the nappy bit. poos are easier to clean from a pocket nappy -cos not as many creases to get stuck in. AI2 slightly easier to pull apart and put together. both can be made as absorbent. if you look at itti bitti- they have 2 boosters- one snaps in from bottom of shell and one from top, and you can also add other boosters that just sit in the shell.

I have a press stud kit from spotlight, which should be able to go through 1 layer fine, but I guess if you are making an all-in02 you only have to attach them to the pad and the suede/microfleece layer anyway? And what is the difference between press studs and snaps?

i have only used the kits (where you use a hammer to attach) on pjs and they would be pretty hard to use with thicker material or multiple layers. if you can access a snap press, it would be worth it, i have never had a prob with snaps put on with a snap press. the snaps are quite cheap.