I guess, you would have to evaluate what you want. Like for example, if you want UV protection and to avoid glass from fragmenting (unless urs is laminated, in which case, this feature is not necessary liao). Or do you want to keep the temperature of the car below a certain level.
I think most car manufacturers take into consideration that some cars are parked under the sun all time time (like my car, the only time got roof over it is when i park in basement parking of shopping center). As long as the plastic is properly maintained with plastic care items, then it should be pretty hardy.
I personally have not installed e-vent, so I am not sure if it is flexible enough to adjust the temperature threshold so that it keeps your car cool at your desired temperature. Another point to note is that, it drains your battery as your car engine is not running when e-vent is operation. How will the constant discharging and recharging of a battery affects its life?
In the case of tinting, a car with good tint would still be hot if parked under the sun the whole day. However, it cools down way faster and your aircon works less to maintain the specified level of coolness.