I use railgun on my "assault" bomber with concussion missiles. It also tears them apart, but I feel the railgun is less useful because people always seem to hunt it down and blow it up.
Railgun is significantly more noticeable. People are trained to hit the "target last guy that hit me" button (R, I think? I dunno, I use W) when they see that railgun splash across their HUD. With interdiction drones, if you don't pop it before it does something, you find yourself in much less of a position to pop it.