The PVB that all windshields are laminated with already blocks all UV A radiation, and glass blocks UV B, so there is no UV benefit to tinting a windshield, or laminated side windows. Some films can block infrared which will help with heat at the cost of visual acuity, but nowhere near as much of an impact as a window shade. The infrared blocking films are the same principle as "low-E(missivity)" glass, but the metal sputtering process does degrade the clarity of your view, and the synthetic film carrier does the same. All the films I know of will also block a significant percentage visible light, a bad thing at night. Film will also scratch much more easily than glass, often even wiping with a paper towel will damage them.

IMO the trade-offs for a film don't outweigh the benefits when it comes to coating a windshield.