We've tried both the Pro Comp and Auto Spring Add-a-Leafs on our own trucks, and have had similar results with both. While there is some gap between the Add-a-Leaf and the rest of the leaf pack, it's mostly due to the anti-noise pads on the ends of each leaf than any design flaw. We have not had the opportunity to try ReadyLift's Add-a-Leaf Kit yet, though hopefully we'll get a chance here soon. Overall performance and ride quality is similar between the Pro Comp and the Auto Spring Add-a-Leafs.