Hmm, tough one. The lure of a flexible / more suitable teaching career against entering the "Free school" minefield.
For me, no. Because it's a matter of principle, for me, that the Free Schools are taking away from comprehensive schools. Both funds and resources. Also, the QTS isn't necessary, so you don't know who you'll be teaching with. Witness the Head of the recent Free School who isn't even a qualified teacher. Plus the employment contact is up in the air, more private than public sector. I don't think you'll have the protection you would in the comprehensive sector.
On the other hand, if you are pro the idea of Free schools, and willing to take a punt on it, it might work for you.
I don't think it will necessarily prohibit you from moving between types of school, any more than the current system prohibits teachers from moving private/ comp. Although you'll still have to take into consideration the subject need / shortage in your local area, of course. You can easily explain to employers why you made that decision, so I don't think you need to worry. However, Free Schools are untested, unregulated. Of course, "normal" schools fail too, but being in a Free School that's failing, (or being successful!) would be a new experience for everyone, I'm not sure i'd be up for that post baby, i'd want familiar.
That said, all my request for reasonable part-time post baby fell on deaf ears. I'm not sure i'd have resisted the lure confronted with wee baby on one hand and close to hand career on the other.