Field Assessment
Underneath the finish, this is the Morgan Revolver everyone else carries. Rockstar hasn't confirmed a mechanical difference, and nothing about the Ultimate Edition announcement suggests one. What changes is the look. A Vice City treatment on the frame and grip, the kind of cosmetic work that says Ultimate Edition without needing a tag on screen.
Both protagonists get one. Jason and Lucia each walk away with their own Morgan Revolver, styled the same way, plus a personalized variant of their own sidearm on top of it. Three weapons across two characters, all locked to Ultimate Edition from day one.
Whether the styling is purely cosmetic or carries some small stat difference hasn't been detailed. Rockstar's announcement covered what you get, not how it performs differently from the standard version, if it does at all.