Hi I dont have any experience of GCSE RS but I did do citizenship. At my school it got about a quarter of the teaching time of other subjects, like RS even tho both are short courses. For revision I barely did any tbh, I watched a few videos and did a bunch of flashcards+mindmaps from the spec but in comparison to other subjects I hardly revised. The exams are always a bit hellish, youre expected to write so much for so little marks on the written papers and the question can be confusing- I literally thought I was gonna get a 5! However there is a multiple choice paper which is nice. Anyhow, I somehow ended up with a 9 (literally on the boundary lol) which surprised me. As a subject, I had absolutely no interested in it, I think if I had been interested then revising would have been much easier and more productive. Best of luck with your decision and would be happy to try answer any questions if you have them on gcse citizenship.