Everyone I know with children there is very happy with it. The reason it's so big is because it's so popular! You'll need to be in (or very close to) catchment to get a place because as far as I know it's always over-subscribed.
Size can be daunting - 300 children per year, not the biggest site. However know of lots of children/parents very happy there.
Catchment stretches right down to Slough fringes so quite a geographic spread. Results v respectable given it's a 'secondary modern' - 64% A* to C at GCSE inc English and Maths. Friends with dcs who just missed the 11+ seem happy with how streaming works. Head is very dynamic.
If you want to look at somewhere smaller, Amersham School is becoming much more popular.