Hi nik,
Potantially any physio you speak to could give you a different opinion, not surprised the head is battered! Generally, i would only use orthotics as a temporary measure and normally as a last resort (in non-surgical treatment/rehab).
Truth is, any trainer (even the most cushioned or motion control trainer) will be absorbing less than 10% of the forces created through your body when running. Now, that 5% could be the difference between getting injured and not getting injured.
But I think a better trade-off can be had by not just looking at feet but the rest of the body as well to see WHY you are 'over-pronating' or have flat-feet.
Feet are supposed to pronate when running, its part of nature's shock absorbtion in the body. Trainer manufacture's and some therapists use the term over-pronation as a diagnosis, but I (amongst others) think its just a symptom for something else.
Tweaking your running style e.g. shorter strides / less heel strike or getting treatment for stiff hips and ankles may do far more for you than any type of trainer or orthotic.
Hope that helps!