Probably the best explanation of the two systems.
As he first points out, both are measurements of angles, not distances (inches vs centimeters). Some relies here have mistakenly mentioned the inches vs cm debate.
An excellent point he makes is that the MOA system actually has finer adjustments; 1/4 MOA is smaller than .1 Mil and with some scopes offering 1/8 MOA, that makes the .1 Mil seem huge in comparison. So if you want absolute accuracy of POA and POI being the same in longer distances, the MOA system is more likely to get you to your goal. With MRAD, it is possible that one click up is too high and one click down is too low. Not a big issue for punching paper or steel, but it could be the difference in a one shot kill vs a wounded animal that gets away.