hi! don't know if this will be of use as i study at an online school however it's fairly similar so i'll share my experience anyway. i've been enrolled in it since 2021, all was fine until last year as i did bad for my y12 mocks, so i'm currently retaking the year (still enrolled in the school) but studying independently as their teaching methods just don't work on me!
revising on my own took getting used to. u have to be v organised and structure things well, obviously there's no one to explain anything so u'd have to be pretty determined or it won't work. i basically failed last year as i underestimated the huge difference between gcse's and a levels. this year i ended with predicted grades of AAAB so i'd say it's going pretty well. without the constraint of skl, u get to work at a pace that works for u and not the whole class which is great.
my major regret in transferring out of traditional school was the social life. i'm not a social person and pretty introverted, although i've made a few online friends, all my irl friends are back from when i went to normal school. i guess if ur social or attend clubs or extracurriculars this probably won't be an issue.
as for exam centres, i used tutors+exams for gcse's. they have a few centres around england and they'r easy to register with. i think i ended up only registering in jan-feb, so a few months before exams, and i had no issues however that was 2022 so i've no idea if things have changed since.
i think if u decide to be a private candidate then definitely plan and structure ur time well! it gets demotivating at times as u have no peer support and ur not around people studying the same as u. but there are a lot of benefits so if ur determined, hard working and don't mind the much reduced social aspect then u could 100% make it work.
however personally i preferred the social aspect and am trying to get back into normal school for y13
