A lot of people are using Mark 5's with good success. Most my friends (including some of the best competitive shooters in the US) shoot them and love them. It's not surprising to me at all that the shooting school is using them with good results.My son recently went to a Long Range Shooters of Utah class so I asked him about their inventory of rifles and scopes.
Nearly every rifle was a custom, about half chassis, half stocked. The scopes were mostly Leopold mark5, a few NF.
Funny they have such bad equipment but he still hit the milk jug challenge at 1k , managed to hit at a mile, and had the smallest group in his class. All with a 6.5 needsmore and a mark 5.
I don't own a mark 5, but maybe I should.
I have also watched some of those same shooters check and adjust their zero every morning at matches. They aren't typically really far off, but two or three tenths is common.
I have been so tempted to buy a Mark 5 so many times but I've just watched too many people constantly need to adjust them.