My humble opinion here only.
To me, tinting is a means to reduce IR penetration into the cabin. This keeps the cabin cool.
I am not sure if the darkness of the tint is a direct correlation to IR penetration reduction or not, but I do know that price of tint has a direct correlation to the IR reduction capability.
When I had my Model Y done last year (December), there were three options available:
- 12% IR heat rejection/40% Total Solar Energy Rejection for $295.00
- 77% IR heat rejection/61% Total Solar Energy Rejection for $695.00
- 96% IR heat rejection/66% Total Solar Energy Rejection for $990.00
All these were XPel film, which I believe is highly regarded.
I chose the last option. These were all available at Tinthaus, whom I would highly recommend - they did an awesome job on the tint, and PPF on the front/graphene coating on the rest.