The existing tinted windows are designed to keep the interior cool Si (thats why they have solarguard written on them) try driving in the sun with the window down and the sun on the side of your face, then wind it up, instantly it cures the burning (i'm sounding like i'm talking to a noob here

)
Had tints on my old orion, medium level all round (minus windscreen) it was great in the summer as the car was cool inside (unless you had it with the non tinted window facing the sun, then it was like a green house) offered a bit of privacy too (usefull if you made a faux pa at the lights and wanted to hide your shame

) security issue is a double edged sword, one its good security because people can't see in and if the window is broken the glass only shatters but is held in place by the film.....however its swings and roundabouts because people think you have something to hide so brake in anyway, are up to no good (especialy the boys in blue....who don't wear blue anymore) and in some cases the film makes it harder for emergency services to get through the glass to help people.
There are proper security films available too that work even better at
preventing forced entry (
waits inuendo)