The main reason tinting is illegal in most jurisdictions is simply that it makes it difficult for cops to see what you're doing inside your car.
Secondary, personal reason: it feels like you’re wearing sunglasses, day and night. Especially for shoulder checking during lane changes. Too, if I was shopping used, aftermarket tint would be a deal breaker, maybe just me though. yeah I know, Great White North.
Just got all my windows tinted, including the windshield. Definitely a difference with full sun. Windshield is almost clear, very slight tint. I'll post a pic when I get a chance
from Llumar.com “Llumar AIR Clear Window Film Like the look of your vehicle as-is but want to upgrade the performance of your factory auto glass? LLumar® AIR clear window film is the solution. It has the same, proven nano-ceramic construction used in premium auto tint, minus the window-darkening color.” From what I can determine it still reduces a small amount of visible light transmission but reduces a good amount of UV and IR.
What brand of tint? I’ve used 3M on my previous cars since the early 90s no issues whatsoever. Thinking of trying Xpel on the Prius, only because local vendor uses that brand. Reviews were also acceptable for that brand.
Here is a comparison of 3M Ceramic IR 70 and LLumar Air Series and Llumar Stratos 70. Llumar Air Series 3M Ceramic IR 70 - The lightest 3M Ceramic IR Tint I have come across. In summary it looks like LLumar Air 80 block 90% of the infrared energy but transmits 20% more visible light. Another option is Llumar Formulaone Stratos 70 - from what I have read it is slight bluish tint and more expensive than Air tint. 8% more visible light as the 3M ceramic IR 70 with the same infrared energy rejection. I have tinted all my windows with 3M ceramic tint with the exception of the windshield and panoramic glass which I hope to do soon. So far very happy with the tint I have. The air looks like a nice option for the windshield especially.