First world problems. Scrap that, American problems. Making this an 'official' condition will only further damage the reputation of an institution already deemed frivolous in the eyes of many.
First of all, you can get Postbox for free via MakeUseOf.com's rewards program. Just make a few helpful posts in the tech help section to get enough points.
I've been through a number of car mounts throughout the years, and they are all lacking in one area or another - they block your vision, they're insecure and the device needs to be actually secured, usually with a clamp of some kind, which you must release via a button.
Pic annotated, so here I'll just say, "elderberries."
iCab Mobile. It's got the most features, including being the only one with userjs support, albeit in a roundabout way.
