Sorry, will reply individually in a bit, but here's a short pros and cons list about St John's (my personal opinion):
What I found great:
The grounds are gorgeous. Acres and acres of beautiful parkland, fields and ponds. They used to even have horses there in the past, but don't have them anymore. I found it quite therapeutic spending time there and you really see what you're paying for.
The kids are very nice. All the ones I have met have been lovely, polite and the parents (those I have met) were also very nice and normal. The majority of kids are quite studious.
All homework always gets marked and there are constant tests and assessments to ensure kids don't fall behind. The teachers have high standards and are very strict on bad behaviour.
GCSE results are great especially considering it's not extremely selective.
Price/sports - it's the cheapest of of the London independent secondaries as far as I know because they get subsidised by Arsenal football club I believe (although I'm not 100% sure on this). There are a number of footballer's kids there and many kids play in the Arsenal academy. They are the U12 National champions. Although they also do a lot of athletics, so it might actually suit an athletics kid. There is even a bit of horse riding at Trent Park.
The family that owns the school clearly care about it a lot and invest a lot of money in its facilities. The sports hall and changing rooms for example are brand new and clean. They are building new classrooms and a new library and the sixth form building is beautiful with a pool and fitness studio. All grounds and facilities are very well-maintained.
The bus service is amazing. It's door-to-door and the driver even agreed to drop my daughter off at her out-of-school activity in the afternoon (although it was close to the school). It's really convenient.
They do great trips abroad and even did an amazing ski trip during the more uncertain times when most other schools cancelled theirs.
It's small and quite intimate and the Head gets to know all the kids.