I think it depends on your other options. The only parents I know who opted for their local free school were ones who knew the only other school they'd qualify for was one they were keen to avoid. If you have an excellent alternative it would be much more of a gamble than if you have no local school to go to or only a poor one. That said, some Free Schools have an ethos or approach that appeals to some parents (it varies of course from school to school) and become quickly very popular.
Our other 3 options are all very different - in every aspect (size, faith/non faith, academy etc ) but ofsted outstanding and get excellent results. Even the least favoured school is ok - not great ofsted but people seem to like it. Hence such a dilemma
I think the thing to realise about Free Schools is what they all have in common. They are being explicitly being promoted by the Government with the idea that there is no common model, with each school being different, at least potentially. So in theory, what they have in common, is that they have very little in common! Other than being state financed. They are free, or at least the relavant sponsor is free, to choose the curriculum and choose the staff (who need not be qualified, again that is up to the sponsors of the Free School). one of the ideas behind this is to bring a greater diversity of chouce in what indeed becomes "the education market"
In practice this means that there are already a number of different types of Free School.
So for example, and these are actual examples, there is a huge difference between a school being set up by a group of parents in an area where there is a shortage of school places, and a school being set up by a commercial company in an area where there is no shortage of places, but a really valuable site which the company is going to get for nothing..
This does introduce an old principle from the commercial world into the world of state education.
"Let the buyer beware."
And of course this has always been true of independent schools.