I suppose that as a parent of two CHB boys, I should wade in here.
I can't really think of anything to complain about, which is very unusual for me.
I am, in all honesty, a prolific complainer - in all walks of life.
It also takes a lot to make me impressed by a school - I'm ashamed to say that Ds2 attended 4 different Primary schools (5 if you count his nursery year).
I had been told that CHB gets by on the strength of its pupils (and clearly they are among the brightest boys around) and that teachers are old-school types who sit and have a snooze in lessons. Actually, there are many genuinely great teachers there who give a huge amount of energy to the boys and are fully committed to them and the school. I've been very impressed with many of them.
For a very bright boy, it is an ideal school, and it is as if the boys are almost picked up and carried by its ethos, standards and vision for them. With a busy life and three other, younger children, I have little time or ability to keep watch over my older boys or even help them at all with homework.
I worried about my ds2 joining, who was in all honesty, terrible at ever completing Primary school homework (both I and the teachers just ignored this, to be honest). Yet he has happily surprised me by his ability to just get on with things himself, and complete work so neatly and with so much diligence (he was a naturally very messy, haphazard child) that I can hardly believe it. I believe this is down to clear expectations from school.
Another thing CHB has given my boys is a sense of respect for others and self respect, and good manners and self confidence.
Granted, many other Grammars may do the same thing, but I wouldn't say there's anything to worry about at CHB.