Hi Jack (don't say that at the airport),
I have both systems, though I think the Fuji Quickload holders are made a bit better. There have been some issues with a bad batch of the latest Kodak Readyload holder, some having a bowed end that may or may not affect film flatness. My Kodak Readyload holder is the last version during the transistion of two sheet Readyloads to single sheet, so it has the black pressure plate; and I am happy to report works fine with the newest films.
I consider each system holder as a back-up for the other system. While Fuji film work best in the Fuji holder, and Kodak best in the Kodak holder, it is possible to mix an match. However, if you make a mistake and get the film backwards into either opposite system holder, it will very likely jamb on you causing a need to disassemble the holder to get the film out.
Kodak Readyload film does seem tighter in a Fuji Quickload holder, so there may be some potential to jamb the film, perhaps depending upon construction tolerance of your holder. The Fuji Quickload film in the Kodak Readyload holder seems to work looser, though maybe it is too loose (film flatness issue?). It might be best to plan on getting both types in order to use film from both companies, at least to play it safe, and allow for back-up gear.
Ciao!
Gordon Moat
A G Studio