Are mirror tints illegal?
On cars? Yes. It reflects light, whether it is headlights or bright sunlight, in other drivers eyes.
Cars, yes it is. You might get fined for that but for windows in your home, I'm sure its okay.
Depends upon the windows involved. You should really write clearer questions to get clear answers. But, if you want really dark tent you should move to Georgia and..... well, you get the picture.
Depends where you live but in many places it is prohibited.