I'm going to say that we are lucky to have these grammar schools within reasonable proximity to where we live. Thankfully, there is no catchment area for Colchester/Chelmsford grammars because, if there was, my son would probably not have got a place. It wouldn't bother me if they weren't super-selective schools either; it's the fact that places are open to students regardless of where they live that matters to me.
The good local comp schools have catchment areas so it makes it much harder to get a place. This is okay if you happen to live in that area but not so good if you don't. The alternative being, to be given a place at a school that you don't actually want but that, unfortunately, happens to be your local school.
I feel that many parents either have to put up with a school that they don't want or make serious financial sacrifices for a better education for their child because they just happen to live in the wrong place.
At least by having no catchment area, it's a fairer system for all. Just my opinion of course.