Sounds like you decided already but here’s what I figured from when I was looking at this question:
Assumptions: You will be doing tactical style shooting with a reticle using a mil or MOA based scale
If you plan to use reticle holdovers but don’t plan to dial at all you can get away with a mil reticle and MOA turrets otherwise I’d avoid a mixed scope.
Some guys say MOA is imperial and mil is metric but that’s not really the case, they are both angular units of measure with no units. 1 MOA 1/60th of 1 degree which coincidentally ends up being almost 1” at 100 yards distance (actually 1.047”). A mil is 1/1000th of the distance to the target, so it’s 10cm @ 100m, but it’s also 1” @ 1000inches, or 1ft @ 1000ft. Either way it doesn’t really matter if you just stay in angular measurements. That is to say for example you make a shot and miss, the correction is called as 2 MOA up 3 MOA left so you make those adjustments on your reticle or your dials and retake the shot. Or you use mils and your call and adjustment is maybe 0.3 mil up and 0.2 mil right. If your spotter uses a riflescope or a spotting scope with a scaled reticle you use the reticle to measure the correction in mil or MOA and then make the correction in mil or MOA. There is just no reason to convert to inches or cm.
If you are going to use your reticle to measure the target and back into a range you could use either, mil is maybe a little easier, the formula is easier to do in your head but MOA is also pretty easy depending on the target. Say you range a 8” plate and it appears to be 4 MOA. 8” target/4 MOA = 2” per MOA = about 200 yards. Of course you’re S.O.L. if you don’t know whether that target is a 6, I or 10” plate. The same caveat holds true to mil based estimation. Assume that’s a standard IPSC silhouette when it’s actually a 3/4 scale silhouette and your range adjustment will be off by 25%. Garbage in = garbage out. Can you tell if that’s a big animal or a small animal? Big rock or small rock? Big bush or small bush?
One other factor is we measure precision in MOA, no one talks about shooting a 0.2mil group, it’s all MOA, sub-MOA, etc. You can judge your hit probability easier I think when you are looking at a 2 MOA target and know you have a 1/2 MOA rifle.
Mil seems to be more popular among PRS shooters but MOA is probably easier for the guy target shooting. In the end I thing what matters most is if you’re most comfortable with ones and tenths or ones and quarters and what your spotters use so you can speak the same language.