I have the Excalibur 21" and like the top feed because it is easier to see the hole I want to cut. It takes a little getting use to putting the blade in the bottom but you soon get the hang of it. With the bottom set screw set into the slot, I just push the blade in on the side it is on until i feel it hit the screw and then move it to the right ( setscrew on the left side) and push it all the way in and tighten wing nut screw.
Allen