I studied Further Maths last year and thoroughly enjoyed it.
The best way to decide is to have an idea of what sort of course you'll want to be studying at uni. If you're like pretty much every GCSE student and don't want to think that far ahead, pick A-Level subjects that you'll enjoy (at some level) for the next two years and will lead you to a field that you'll be studying 3+ years after that.
You've said that older students have recommended against studying FM, is that possibly because the FM teachers are boring/your school doesn't teach FM as much as leave you to it?
FM isn't for everyone, in my year, out of the 15ish students that started, only about 8 got a full A Level in FM whilst the rest decided to only study half the units for an AS Level.
Not completely sure about this, but I think the A Levels have changed recently, so not sure if you'll be doing modules like D1-2, M1-5 etc. Check on this/keep in mind for other replies
Good luck with your GCSEs and future career
Not true. Based on what I've seen FM may benefit Engineering courses more than Maths in first year.