We moved house to be in catchment for an outstanding secondary with a great pastoral reputation which was also strict on discipline. We kept DCs in their outstanding primary school a few miles away.
When Ds1 (now year 11) went to the secondary everyone, bar a few children who went to a grammar school, went to the feeder secondary. Ds1 had 1 other child who he knew but wasn't friends with go to his school.
Ds2 went with absolutely no-one. He is now year 8. Both have made incredible friends, neither have missed their old friends at all.
It could be that your child's best mate ends up going to a grammar school or moves away because of a parent's job.
My son's secondary ran an extra morning session for all children coming from schools outside their usual area, so we lived in catchment but the primary school was miles away. That way the children would have some familiar faces before the year 6 day in July where they all spend the day in their new form in their secondary school to be still wearing their primary school uniform.
In year 7 a lot of children will come in with no friends and school do everything possible to make friendships happen. In fact ours has a forest day where they do team building and they deliberately split up same primary school children to give them a chance to meet new people outside their usual friendship group.
These are the questions to ask at an open day/evening. We attended in year 5 and 6 to get a good feel for the place. Plus we booked an appointment to speak to the head of year 7 transition to see what measures the school put in place for children like my son.