If I were choosing a new place to live, knowing in a few years my DC would be choosing secondary schools, I would probably not go into a Grammar area, but if I could afford it, move close to a great Comp that I knew they would get into - this would probably mean lots of research and moving very close.....and yes I know that schools slide in success and boundaries change.
The thing with Grammars, is that unless your child is exceptionally bright, you just cannot know they will definitely get in - there is no certainty and even less certainty in a super selective area. People on MN are always saying their child is on the top table or top of their class and asking if that will be good enough for grammar. The trouble is that no one knows for sure - some top table children get in and some don't. It's difficult to be precise about exactly how clever our children are, whether they will be 'clever' in the skills tested and if they will perform on the one day. That is a lot of uncertainty. The tutoring and rigorous home prep that happens is a way parents use to try and reduce the uncertainty, but it cannot remove it, as every year, many children don't get in, obviously. And as we know, increasingly it's children who are prepared who get the places ....dispelling the idea that a tutored child will then struggle at garammr ..... well some might, but the majority have had some coaching. In superselective areas you need to be super bright and super prepared to really have a chance.....and it's not possible to know for certain that they will get in.
And the question is, do parents really have a back up then that they can honestly say they are happy with and tell their children honestly that they are happy with, and move forward without feeling they are getting second best? Many people don't have that back up that they are truly happy with....and it's for this reason that I think Grammar areas are best avoided if possible. No one wants their kids to feel they are getting second best or are second best at 10, and it's not good for the parents either.
I think it's a bit different in a super selective area, esp if you aren't very near to the grammar, or very few go from anyone area, as the vast majority will go to non-Grammars anyway. It's a bit different if you have Independent as a back up and you really would be happy with that. It's a bit different if you have an over the border possibility of a Comp. however, if you're in a full grammar area, I think you have to be somewhere where the sec mods are great and absolutely not second best, to be able to genuinely feel okay about them. Great if that is the case, and if not best avoided in my view, especially if you would want it badly, because most won't get in.