Howdy
Schofield's are relatively rare in CAS. Most shooters use Italian manufactured colt SAA replicas, or Ruger Vaqueros. The rest use a smattering of Italian made Remington replicas, Cap & Ball revolvers, American made USFA colt replicas, and real Colts, along with the occaisional Schofield.
I'm not saying there is anything wrong with the Schofield, it is just unusual to see one. I have cut down a bit on my cowboying over the past couple of years, but I still manage to get to one or two matches a month. I'd say I probably only see one or two Schofields a year, I see hundreds of clones and Vaqueros. Unusual guns are always worth extra 'style points' and Schofields certainly rate high for style points, right along with Henry rifles.
One of the percieved advantages of the Schofield design is that it is quicker to load and unload on the clock than a colt style Single Action revolver. But it is relatively rare to actually encounter a pistol reload on the clock in CAS, so even though the Schofield is truly quicker to load and unload, there is not much real advantage gained.
The Schofield has a different grip shape than a colt style SA, and the distance the thumb needs to reach to cock the hammer is greater than with a colt style SA. Since most CAS shooters hold their revolvers with two hands and cock the hammer with the hand that is not pulling the trigger, this does not present much of a problem. However I shoot all my CAS pistols one handed, and I find it a bit awkward to reach forward with my thumb to cock a Schofield hammer. That is probably the biggest reason I decided early on that the Schofield was not for me.
The modern Schofield's, both those produced in Italy and the recent versions produced by Smith have had some very minor design changes from the original Smith design. Although these minor changes have not affected the gun's ability to shoot Smokeless powder, they have have rendered them very poor Black Powder performers, if you are at all interested in shooting Black Powder. Unlike a Colt, clone, or Ruger, the modern versions of the Schofield bind up very quickly when shot with Black Powder. The great majority of CAS shooters do not shoot Black Powder, so this is not an issue for most.
One other point. You mentioned you are interested in competing in CAS using 'a' Schofield. It is pretty universal in the CAS world that two revolvers are required. Nothing says both revolvers have to both be the same. Still, if you want to buy a brace of Schofields you will probably wind up spending more than you will with a pair of SAA clones.