Assuming your going to use it on a Springer, I don't see it specifically saying the Sidewinders are airgun rated like Hawke says on their website for the MapPro and the Airmax models. You may want to e-mail Hawke and see if using the Sidewinder on a Springer voids their warrentee.
I think both reticals have there advantages and disadvantages, and it comes down to what your targets are going to be.
True Mildot scopes can be ok, but for use as aiming points for hold-over and windage, I find the dots kinda big to be as precice as possable on small targets at longer ranges.
Their SR6 rectical can be used with their free download balistic program, which will usually get you in the ballpark better than doing guess-timates, but both retical types should realy be field tested at known ranges to get the true drops for that gun/pellet combo.
Paul.