Just a note on magnetic numbers. I thought a couple of tips would help.
Ovals are less likely to grab air and go flying off like a frisbee. Some shops will say that you don’t need tape on the leading edge but that’s under normal use. The turbulence between 2 cars going 200 kph up the back straight is considerably higher than road use at the speed limit. The closer you are to each other is the higher the air pressure between you. So… no matter where you buy them or what they look like, if you use blue painter’s tape on the front edge, you will be less likely to buy them again.
Remember that they aren’t a fashion statement. They should be 6″ high, contrasting colors and an easy to read font. They are a safety device.