I usually tell people to a.) Study math b.) many people find mils to be easier conceptually. 1 Mil is 1/1000th the distance to the target whether you’re using yards or meters. At 100 yards 1 MIL is equal to 3.6” and at 1000 yards, 1 MIL is equal to 1 yard. But also, that most people don’t need either one, use terms you understand even if that means yards and quarters because it doesn’t matter if your rifle is 1MOA of you can’t visualize it. If you can visualize group sizes at distance based on the size of everyday known objects, use that. And no, mils aren’t metric but they do correlate closer to metric than imperial.