Remember a Fliter is just that. It is also a 'p2 sift' to decide early on whether you have the necessary basic qualities. I believe it is a single interviewer whereas OASC is a 2-man team. One questions and the other scribes and then they swap over.
I was asked a real stinker of a question and I still don't know the right answer. They refered to another candidate and asked whether I could envisage working with him and living in the officers mess with him.
The candidate in question had a 'cut with a knife' accent and was almost impossible (delete almost) to understand. I thought at the time that it was an entirely improper question. I never saw him again. Also the wg cdr, at one point, scored points off the sqn ldr.