I have a few friends that have them. They like em. It doesn’t take much effort to remove them since they screw on. If you’re going to a car meet, its easy to take off so you can have that “clean” look.
There are several brands out there, I’m not sure which ones my friends have. Turner sells them. http://www.turnermotorsport.com/c-283-bmw-license-plates-brackets.aspx