So another question that just popped in my head, thoughts on MIL vs MOA starting out.
I tried a friends MIL and it just never clicked for me like MOA, but since he doesn't know MOA it might be better to go MIL.
I would use what you BOTH use best. Because one of you will probably be the spotter and need to convey corrections to the shooter.
I think in inches so I use MOA. 1 MOA = 1.05" at 100 yards. 1 MIL = 3.6"
Almost all paper targets are in inches too...
I use a MOA reticle a lot to measure my groups on a rock face when I shooting maybe 700~800 yards. Since basic rifle accuracy is determined in MOA, it is easy for me to determine how my group size on the rock equates to desired accuracy. If I measure a 1/2 MOA group at 800 yards, I having a great day!
MILs work great for PRS shooters because you use less numbers when communicating. As in 12.5 MOA would be just 3.7 MIL. (I think)
Young minds learn better too....