Though it's not a .380, I had a PM9. Loved the gun, but ended up trading it for a P45. I recently picked up a CM9 (Still have the P45) & honestly, can't tell the difference when shooting it. I fully understand that the CM (& the CW series) have pinned front sights & standard rifling barrels, but I couldn't tell the difference. IIRC, Gunblast ran a comparison between 2 Kahrs (Polygonal vs standard rifling barrels) & actually got slightly faster velocities through the standard barrel (I think accuracy was the same). In such short barrels (3-3.5"), I don't think you're going to see any real advantage with the polygonal barrel. I will say that the slide on the CM/CW series is sharper & definitely not quite as nice & smooth as the PM/P series, but I didn't notice any functional advantage.
I do prefer the look of the PM/P series, but I'm not sure they're worth the extra $.