I apologize for not mentioning that sizing fired belted case bodies down all the way to their belts only gains about 1/4 moa of accuracy. It'll cut 1/2 moa ammo's accuracy by 50%. If the best you and your stuff do is much greater, it'll be much harder to see the advantages of Willis' collet die.
It's like many tools and techniques that separate those on the medal platform and others in contention from everyone else playing the game. Some understand and benefit from it and the rest just keep on doing their own thing.