I understand that the Shotgun slug has tactical value. It knocks people down with one shot. I is cost effective for sure. But the weapon in general has its draw backs. Just working the pump action under stress can be difficult.
One of the guys on my department was involved in a shooting. He shot the suspect two times with a slug. However he short stroked it after the second shot and the gun malfunctioned. He thought it was broken, so the threw it on the ground. You may think that this is a simple training issue, but I can tell you that this officer was high-speed low-drag.