Several weeks and some 600 miles ago I purchased a set of M2 shocks that were tuned to my specifications (rider weight, style,etc) to replace the originally installed Fox shocks.
Installation and initial adjustments on my 2015 STS was straightforward, per the illustrated instruction package.

The M2 shocks have markedly improved both the ryde and handling on freeway and secondary roads. I'm no longer experiencing riding on the bump stops on my daily canyon commute, and on good roads at freeway speeds the nearly frictionless shock action results in an extremely smooth ryde.

The M2 shocks are real eye candy with blue springs, machined ride height adjusters, and cleanly machined shock mounts. The ride height and valving adjustments are easily changed for those of us who simply can't leave things alone. They are also re-buildable.
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I'm going to put the M2 shocks in the category of “you get what you pay for”. Excellent workmanship, good documentation, and improved performance.
Based on my purchasing experience, Mr. McBain also provided a superior level of customer service and support.