The FCD was not meant to improve accuracy and it may actually decrease accuracy with some bullets/head stamp brass.
The primary purpose of FCD is to ensure out of spec/out of round bullets and cases are "fixed" so they will reliably chamber in any barrel, factory or match.
Secondary purposes are seating/crimping in separate steps and push-through resizing overly bulged cases regular resizing dies cannot fully resize all the way down to the case base so they can fully chamber.
Of course, if you are using within spec jacketed/plated bullets typical of jacketed diameter (.451") and cases that are not overly bulged, FCD's carbide sizing ring won't do much for you unless you want to seat and taper crimp in separate steps.
If you plan on using larger sized lead bullets (.452"+), the FCD's carbide sizing ring may post-size the bullet which may reduce neck tension and increase leading. Inconsistent chamber pressures and leading will likely result in decreased accuracy.