Obviously these are excellent, rugged scopes, and are being used by the US military.  The Marines use it on their DMR, and the Army on the SPR.

The M1 turrets are better for bench shooting, as they offer 1/4 MOA adjustments.  But the M3 setup is much better for field use, as they are much simpler and faster, and the lack of such granular adjustment isn't much of a hinderance.

To elaborate, with the M1 turrets, you may need to rotate the turret two-and-a-half rotations to get the desired elevation.  Not a problem on the bench when you have plenty of time to set up your shot.  But in the field, will you remember what distance it was set on last time?  ("Did I go 1.5 or 2.5 rotations last time?")  Will you be able to adjust those turrets quickly?  Etc.

With the M3 setup, the elevation wheel gives you 1 MOA clicks, but most loads can be adjusted for out to 1,000 yards with a single rotation of the turret, so the markings on the turret will always tell you exactly what the scope is set on.  And, if you're using a standard load, the BDC function allows you to "dial-a-distance" and be right on.

-Troy