Questions
Does it stay dark when the car is off?
Yes. The film needs power to hold its clear state and returns to tinted when unpowered, so a parked car stays private.
Will this pass a roadside tint check?
That depends entirely on where you are and what level you are running. Tint law varies by state and country and it is your responsibility to run a legal level wherever you drive.
Can a shop fit it for me?
Yes, and most will do it in under an hour. It is a dry application, so any tint shop can handle it, bring the kit and ask for a door-panel-off install.
What happens if one window fails?
Each window runs on its own inverter, so a failure is isolated to that window. Inverters are replaceable without removing the film.