most solar film providers advertise their products to be non-conductive of the signals, so this should be fine.
i don't think these providers will prefer cutting a hole for the in-car unit, it serves more fuss for them. for my dad's car which just installed, they took the unit down before attaching the film, then stuck the unit back up.
regarding the film causing unpleasant reflection at the demister lines, ours is indeed experiencing this just after installation. according to the boss, this is normal, as the film takes sometime to cure.
for example, we were reminded not to use the power windows for 48 hours, and not to activate the demister for 2 weeks. this is because there is inevitably still some moisture between the film and the glass, but it'll eventually dry up as the film is mildly porous. this is why most cars which are just installed with solar films are advised to be exposed to the sun as much as possible to aid the curing.
for the brand, you may refer to my other thread where i gave a brief humble review.
http://sgforums.com/?action=thread_display&thread_id=230272