Rockauto has the OEM Brembo calipers BR3Z-2B121-B & BR3Z-2B120-B for $207 and $225 each. Only one side requires a $50 core charge.
Therefore, for genuine Brembo calipers the cost is $482. Parts from Tasca are about about $85 more
Your O'Reilly versions with paint and decals (partial cost of decals) = $327
That's a savings of $154 but doesn't quantify the time and effort to paint the calipers.
Is $154 worth it? You may get away with it on the street, but if you ever want to take it to a road course don't expect the aluminum alloy used in the knockoffs will be as good as the Brembo's. I'm sure O'Reilly/Cardone/Autozone didn't test it on a track to see if it will withstand flexing and high heat when stopping a 3700 lb Mustang from 120+ mph on a repetitive basis.
My opinion is that these are just ticking time bombs.
Your math is slightly off. I'll be in to these brakes $263.56 for the calipers, paint, and decals; $218.44 less than the straight up Motorcraft/Brembo. I'd be painting the calipers irregardless of the source of manufacture to the grabber blue color as it's an accent color I've been using on the car (was even going to paint the stock calipers before I planned the upgrade). Then I'd be into the Motorcraft/Brembo units for 564.18 with paint. About the same I have into the whole project at this point with stainless lines and pads with everything else.
And what if the aluminum alloy is just as good in the knockoffs? We don't know. I know I'm rolling the dice a little on this; I've mentioned this in an earlier post in this thread. So is $218.56 worth it? It might be! For how I use the car with the occasional spirited driving, it might possibly turn out to be a great economical way to upgrade my brake performance. I also realize it may fall flat on it's face.