Okay; I see 2 downsides to "good sights" on a "belly gun", be that P-3AT, Seecamp, Davis Derringer, Tomcat or whatever.
First is the additional expense everyone pays regardless of whether or not the sights are really effective for the niche this gun fills.
The second, and more important I believe, is the false sense of security/capability they may instill. Even with the best sight system, the .380acp launched from a 2.7" barrel would be marginal at distances where use of sights is necessary. Unless you have nerves of steel, you aren't going to get precision aiming from a gun with a 3.8" sight radius. Add to that the marginal terminal ballistics of the cartridge and I fear over-confidence in what to expect from the little gun. Is an occular shot possible at 15 yards? Sure. Is that a likely outcome in the heat of the firefight? I don't think so, but then maybe you're a much better shot than I am. How far out would you take a shot with the P-3AT? My max range is about 7 yards and the shot would be marginal at that. With my primary carry gun move that out to about 15 yards. Beyond that I have other options to exhaust before engaging the BG.
Hey, if great sights on a hideout gun floats your boat, go for it. If they boost your confidence in the hardware, go for it. But please consider the points I've tried to make and don't go trying to get more out of the little gun than it's capable of delivering. If you envision longer shots when your balloon goes up, then perhaps you should consider spending your money on figuring out how to hide a more substantial sidearm, be that Glock, Sig, 1911, HiPower, whatever.
Honestly the only "upside" I see to good sights on a "belly gun" is that they make punching holes in paper more fun; therefore I'll practice more. Thus developing that muscle memory I mentioned in an earlier post.
Allan