OCR MEI is quite different a Maths spec.: they don't even have similar modules. C3 has coursework (something no other specification, OCR A, AQA, WJEC, CCEA, Edexcel has)!!! And they have all other kinds of modules: in addition to C1-4, M1-4, S1-4, D1-2, FP1-3, there are DE (with coursework), DC, NM (with coursework), NC (although AQA offer FP4, and Edexcel offer M5). Plus the core and further pure modules have real names (not just "Core Maths 1-4"... but "Introduction to / Concepts for / Methods for / Applications of Advanced Mathematics". They also offer Further Maths Additional at AS and A-level (as well as Edexcel).
OCR is much more limited in its range.