I've got a number of Leupold Mark 4 scopes and my favorites are the 3.5-10x40mm series since they offer a good combination of weight, size, optical clarity, magnification and quality with an excellent reticle. I have a front focal plane (FFP) version with a tactical milling reticle (TMR) that came with M1 adjustments. The problem with many of the Mark 4 scopes is that they have MOA adjustments with MIL reticles. I'd much rather have MIL/MIL so I sent the scope below back to Leupold for an M5 conversion which they're now offering on specific scopes. The first thing I noticed when I got the scope back is that the M5 adjustments are WAY better than the M1 in terms of feel. They have very positive clicks (Nightforce like) vs. the somewhat spongy clicks of the M1, M2 and M3 adjustments. I don't know what Leupold changed but it's a significant improvement. The upgrade costs $195 but I consider it to be worth every penny, particularly when compared to replacing the scope with a MIL/MIL FFP scope of similar quality. Now I have to decide if I want to upgrade my second focal plane scopes.
Before the M5 upgrade - Leupold Mark 4 3.5-10x40mm M1 FFP
After the M5 upgrade - Leupold Mark 4 3.5-10x40mm M5 FFP
Before the M5 upgrade - Leupold Mark 4 3.5-10x40mm M1 FFP
After the M5 upgrade - Leupold Mark 4 3.5-10x40mm M5 FFP