I'm of the opinion that you can't ride a plus tire aggressively and have it perform well, regardless of inserts. There's a balance between weight, the stability of the casing, the damping of the casing, and the pressure/contact patch. Plus tires are feeble, vague balloons with no stability and regardless of inserts they roll over far too much in corners and are terrifying on off-camber. Add pressure and they're bouncy/underdamped, unpredictable, and the grip goes to shit. If you make them burly enough to be stable then they're a boat anchor. Some inserts stop a tire completely folding over or...