If you are looking for a great place for numbers go here.
https://www.soloperformance.com/
Dave, the owner, is a great guy and his business sponsors our local SCCA Autocross chapter. He also happens to run a pretty mean Mustang in CAM-C which is co-driven by his daughter.
The magnetic numbers sold at the link above have never flown off my car and I've never seen any other numbers he's provided fall off cars much faster than mine. We've run in pouring rain, blazing heat, and cold windy conditions and I've never lost a letter or a number. He also sells numbers in some form of thin vinyl stick-on static material, but I've never seen anyone use them.
I can't speak for how they'd hold up under triple digit track speeds, but for autocross they are perfect. They hold on tight and are highly visible, something I appreciate as a corner captain call in penalties. I hate having the guess at some the numbers and classes on the cars which use tape.