Zorba,
50% is the lightest we have, if you went ant lighter you wouldnt be able to tell to be honest.
If the police do pull you you will asked to remove them. This is regardless of year of car, the legislation covers all vehicles of any age im afraid.
The film will offer security in that it makes it more difficult to see in and it may hold the glass together but you really need security film which is a different kettle of fish.
We dont do a mobile service as contamination is the main problem with this job and doing it outside would be a nightmare to get the job correct.
Hope this helps mate,
Regards,
Stevie