like someone already said, there are a million articles on MRAD vs MOA.
Its basically the difference between metric and imperial, but it is so much more to that.
Whether you are taking long shots for funzies at the farm, practicing at the range, or competing, if you want to get good and fast at precision rifle, one thing that will certainly help is to minimize the amount of math you have to do, and ensure you are doing math with numbers you are comfortable with.
Either system works just fine. Its all about how you do math in your head. Do you like MM, CM, Meters, Mils, KM, Meters/Second, or do you prefer inches, yards, minutes and miles per hour?
Canada is a bit of a weird country where all our science is done in Metric, but a lot of handiwork is done in Imperial. We estimate our distances in meters, but measure our targets in inches. We estimate our speed in KPH, but estimate our height in Feet.
Many known distance ranges across the country are actually in yards.
No matter what system you are using, you probably end up having to do some conversions, and alot of times its these conversions can trip you or slow you down and have you putting bad data in your scope, or have you doubting your math in your head while you are squeezing the trigger.
In field shooting, where you are denied a range finder, you are estimating distance based on the size of certain objects in your reticle, using the hashmarks and an estimate of its height to extrapolate distance. Most people would do better with metric in that case, although older people are probably still going to be more used to imperial.
The nice thing about metric is everything divides nicely by ten. With imperial there are a lot of halves, quarters and eighths. My dad is a 3rd generation carpenter. Ask him to add 7/16, 1/8, and 3/4 and he comes up with about an inch faster than I can understand the question. It really boils down to what you are comfortable with. Don't over think it.
The other thing to consider is if any competition you are contemplating trying measures their targets a certain way. For example, many F Class competitions the 5 ring is 1 MOA, 4 ring is 2 MOA, 3 ring is 3 MOA, etc. After each shot you get an indication of where you hit, and you can use your score to know how many MOA away from center you are. In that case its probably much simpler to just stick to MOA.
The only thing that I would personally recommend to stay away from, is scopes where the reticle is in MRAD, and the turrets are in MOA. I'm sure there is a good reason for it, but I just can't wrap my head around why you would want to add the extra step converting mm to inches every time, if you don't have to.
Those are some hefty scopes you picked out there. You would probably want to look at a -40 MOA rail, and maybe an anti-cant level as well.