They shoot the same. Carters are louder, generally have smoother pump strokes, and are heavier (so some people find them easier to aim), but once the ball leaves the barrel, it is all projectile motion.
Duckslides are quite nice, if a bit wiggly (this can be fixed). It gives you a very solid feeling and smooth pump stroke, rivaling a Sniper. Besides that, it really just is a $150-200 pump handle. However, the Redux and Carter Duck are just $1000-2500 Nelspots, so whatever.