Hi again, sm, I hope you feel better soon.
I don't know any Year 6 parents at Tyndale, but there's a cohort of middle-class Year 5 parents who are in no position to pay school fees, and who have been muttering very seriously about getting together and all sending their kids to Islington Green. Perhaps you could get ds to canvas his friends on which schools they're planning to go for. Or ask for a meeting with the headteacher of Tyndale?
The new head at Islington Green is apparently v. good, and they very much separate off the Year 7 intake from the older kids. Apparently there a system whereby Year 7 have to do all their homework in a supervised session at school, which can't be bad. The school is oversubscribed, despite what people say about it, but if you live where I think you do, then you should be safely within the catchment area.
The other option for boys is Central Foundation by Old Street Roundabout, which seems to have the best exam results of any boys' or mixed school in the borough, but I don't know anyone else there.
I know it must be hard for you with depression, but a lot of the open days are happening at the moment, so I wouldn't leave it too long, bearing in mind the forms need to be in by 22nd October. Alternatively, the headteachers might be prepared to see you separately and show you round.
If you phone cea@islington, or whatever they call themselves, they do produce a brochure explaining the process pretty clearly, and including little summaries (very gilded, though!) of all the schools. It also has interesting statistics like how may applications there were, and how far away successful applicants lived from the school.
hth -- CAT me if you want to talk.