You best to learn both, but there is no need to be an expert in either.
Majority of the scopes, especially low to mid range, uses 1/4 MOA dials. So there is no escape MOA. Also people tend to talk accuracy in MOA. You hear people say their rifle shoots 1 MOA, how often do you hear people say their rifle shows 0.3 Mil?
But the concept of mil is important. For one thing, a lot of scopes have mil dot reticle (even though the majority of them still uses 1/4 MOA clicks). Reticles with MIL based subtention are far more common than otherwise. If you have been high school educated in New Zealand, you would have learned all your maths and physics in metric and decimals. To think of the height of a person or a fence post, the acceleration of the gravitational pull, in terms of metres and calculate everything in decimal is just far more intuitive.
Having said all that, you can actually get by without understanding all that really well. You just need a range finder and a ballistic app on your phone. Do the range reading and then punch numbers in the app. Voila.
Bookmarks