I've had a number of vehicles tinted in the past. The most important thing to check is the Total Solar Energy Rejected. The higher the TSER %, the more solar heat is rejected. Every reputable manufacturer will publish these figures as part of a table that includes the percentage tint, TSER, IR rejection, visible light transmission (VLT), etc.
The Grenadier has some fairly flat windows. So it should not be that difficult to apply tint to. If the windows or windshield are curved somewhat (usually convex) then the tinter usually has to use a heat gun to "shrink wrap" the tint before final application. Flat glass means no heat shrink, which should lower labor costs.
Also make sure you're using a good ceramic tint.