Currently, I'm in Y12 and I chose to I take core maths along with 4 AS levels (bio, chem, physics and psychology), as I had heard a lot of positive things about it and my sixth form strongly recommended it. I dropped it... or tried to... the teacher is looking for me but I keep escaping as I'm sure he wants to persuade me not to drop it. The main reason I dropped it was because the way it was taught was very slow. I could have completed the work covered in 1 hour in 5 minutes, and being honest, the work was really boring. It was common sense and not hard at all. I would take the exam if my sixth form gave me the resources and specification and allowed me to study at home and not attend the lessons, but I don't think they will allow that.
Anyways, enough about me, now about core maths... It is a 2 year course with exams at the end of the second year. The UCAS points are equivalent to an AS. My sixth form told me that Universities will love core maths and that it's a very good qualification to have and will help with other subjects such as biology and psychology, which is why I picked the subject. I dropped it as I felt the classes were too slow and also I wanted to concentrate fully on my A levels in the second year. If I change my mind and pick up core maths again because the teacher persuades me to, I'll let you know,
If you have any questions, don't hesitate to ask. Also, don't let my opinion put you off of you want to do it.