On the topic of taillight overlays, just dont lol. They are TERRIBLE imo. Nothing beats a properly painted light.
Vision is right about nightshades vs real paint. Nightshades can be done alright, proper paint and clear can be made flawless. A few coats of clear and some proper paintwork and you cant even feel a seam if you only do a section.
As an edited benefit you can wax your tails after and they are a mirror finish!