Meataxe, the issue we owners of the S face is that the Mlok rails they put on the S aren't well thought out. It's impossible to attach handguards in a way that keeps you from touching hot metal with some part of your hand. You also can't attach a cantilevered light mount directly to the mlok. Even if you mount 1913 rails, you can't have the rail as far forward as the 1913 rails on the military version allow. All this because they decided to inset the mlok rails instead of leaving them flush with the screws.
Check out HBI's handguard for the MS. It looks like it solves all the problems for that setup.