It's fair for everyone who is actually taking the AS-levels but unfair in the sense that people who don't do them get ******** predictions. I know a school that used the actual AS exams as mocks a few weeks after the real thing...
As someone said earlier, some teachers would just tell the students of what topics to revise. People who did OCR Sciences this year will know about having to revise the whole textbook twice before each exam. It reminds me of GCSE controlled assessments, mostly fake and easy for anyone to cheat.