In mY particular Judge the discs were not quite as accurate as the buckshot. I like the concept though.
It's simple aerodynamics. Buckshot is spherical, allowing for less wind resistance and greater stability in flight.
Personally, I always thought that the discs were a poor concept for that very reason, but then again, due to a past interest in aeronautics I was immediately aware of the inherent flaws of such a design.
Frankly, the discs are a poor design for the aforementioned reasons. They're unstable in flight due to said design, which reduces accuracy, can affect their velocity on an individual level causing inconsistencies in performance, and can potentially result in reduced damage since it's possible for the discs to hit the target sideways or otherwise turn sideways then remain that way as they decelerate.
There's a reason why this design wasn't already popular, not to mention why no one bothered to copy it after the fact. It looks neat and on paper .40cal discs sound better than .36cal balls, but in terms of actual performance won't offer anything over conventional buckshot.
That being said, obviously they'll still be effective, just not any more effective than buckshot, but rather less so, especially considering that some of the space is wasted on tiny BBs which won't penetrate nearly as far nor deal anywhere near as much damage, ergo it's not worth it to spend any extra money nor choose them over more conventional ammo like Federal Premium .410 Handgun.