In your words of three sides to a story, we do have the truth. Truth is, for us, M2 missed the setup. When the suspension arrived the first time, and runs were made, the M2 setup was far from correct and became a wild ride down the dragstrip. The suspension was returned several times until a ridable, but not a confidence inspiring setup M2 finally delivered. From a rider perspective, it becomes difficult to race at 100% when each pass is eye opening in a bad way.
Consider too, regarding Spyders, and this is not a story of three, but rather proven chassis dynamics. M2 promotes running increased length front shocks. The downside to this on a Spyder with under 5” of wheel travel, is that the suspension movement bump steer becomes increased, which is not good. Also, increased shock length, increases the limits of chassis roll / lean, which on a Spyder is counterproductive to cornering forces. Add to this, if the Spyder ride height is increased, that is excellent for ground clearance, but sadly positions the suspension arms at less than optimum angles and moves the chassis roll center to a less optimum setting. In simple terms, compare a low slung sports car, capable of holding the road thru corners compared to a raised 4wd vehicle. Yes, each suspension company tends to run a firmer spring to help give that planted feel.
All the best with your M2 stuff. Seems concerning though that another Spyder owner needed several times back to M2 to get their Spyders, almost go kart simple suspension, set up. Again all the best with your stuff.