You are correctI find that heat gun on plastic trims tends to make it look better for a bit, but over time it actually does more damage. Plastic is oil-based, so something designed for plastics is preferable and actually provides some protection.
If you want a cheap solution, smooth peanut butter works just as well, and whatever you have leftover can go in a sandwich afterwards. Just watch out for people with allergies.
Maybe 3 times with heat gun and the trims can dry out and become brittle and start to fall apart
The heat gone brings the oils to the surface that's what brings the colour back