I carry a 4516 every day and wouldn't trade it for anything. It's never malfunctioned, is extremely accurate and performs as well as the full size version, the 4506.
Here are the reasons I'd use a 4516 over a 457:
1. It uses easy to find parts that are readily available from midwayusa.com, while the 457 parts are usually on backorder
2. It's steel and isn't that much heavier than the aluminum framed 457. I shoot a lot and like knowing the steel framed 3rd Gens simply won't wear out, the frame rails won't get gouged and there is no anodized aluminum to get chipped
3. If the steel frame and slide get too beat up, it's a simple job to bead blast them to look new again
4. They easily fit in P228/9 holsters
5. They take Novak steel sights that aren't "economy line plastic"
6. I think the lines of the pistol look better....just like a mini-4506
7. It is steel.....steel, not aluminum or plastic.