i've got a maginon bullet cam, a muvi copy and a sj4000.
the maginon claims to be 720 but usually gives 480
the muvi was handy to pop inside your lid but quality rqnged from merely ok to poor.
the sj claims full hd but gives 720.
none of them liked electrical currents too close to them.
btw the maginon survived an 'off' at cadwell and still works fine.
imo i'd rther buy a copy first and make all the mistakes with cheap gear rather than lob a £400 gopro down the road