I did a
review on the Mk 6 M5B2 3-18 a few years back. At that point the optics we roughly equivalent to many $1.5k scopes. Now though I can tell you they don't keep up with
sub $1k Sightron SIII I did a review on last year and although that scope is muck larger than the Mk 6, it is not significantly heavier.
The big thing about the MK 6 is that it is very light and very short but still has ok optics. The issues it has is that it is very expensive and tends to have problems with accuracy in adjustment magnitude. The one I had was 2-5% off out of the box. Leupold fixed this but a few years later it was back to being off again and I sold it part for that and part because I just don't think it is optically good enough for the price anymore. Basically, I think the optical design is just too aggressive on these things and the price is too high.
As for the B2 adjustment, it has a bit of a squishy feel that some don't like. I rather liked the design though. I liked the independently movable outer ring as well as the robust zero stop set screw. Mine never malfunctioned beyond having issues with the adjustment magnitude and I believe that had more to do with the optical design than the adjustment itself.