A keen-eyed reader noticed that all references to the .45/.410 Shot Pistol have been pulled from the USFA website and ShotPistol.com now just redirects to the USFA homepage. Judging by the comments readers left on my original post about the USFA Shot Pistol M4-410 model, pulling this product was probably a sound business decision.
Personally, I loved the weird combination of an old-style frame, oversized cylinder and rifle-style muzzle brake.
[ Many thanks to Aaron for the tip. ]