from traditional double action pistols in general and a couple for switching away from Sigs specifically. The design of the Sig pistols places the center line of the barrel much higher above the center line of the arm than many other pistols. This results in the gun having more leverage to use against you in recoil, causing more muzzle rise than with other guns with a lower bore axis. Sigs also have a fairly long trigger reach and a heavy double action pull. The long reach coupled with the heavy pull can make it very difficult for people with small hands to grip the gun and manipulate the trigger properly for effective shooting. In my opinion, these are the two strongest arguments against the Sig.
As far as double action pistols in general; they are more difficult to train with due in part to the heavy pull of the trigger in double action, and in part because of the transition from double action to single action for subsequent shots. Add to this the need to de-cock the pistol to make it safe and it turns into a pretty tall order to take someone from ground zero to proficiency in the modest training time that most law enforcement undergo. The de-cocker is one of my biggest complaints when it comes to law enforcement firearms.
I have witnessed and testified with regard to many negligent discharges as a result of an officer failing to de-cock his double action pistol after a firefight. This is largely because the average LEO is not a firearms enthusiast and does not practice enough to make this action automatic. When the adrenaline starts pumping, and the heart rate skyrockets, you WILL suffer a loss of fine motor control. You WILL forget things that seem very simple and natural to do, if you have not done them recently and frequently enough to make them muscle memory. It's easy to remember to de-cock while on the range. Not so much after a gunfight and your mind is racing and your heart is pounding.
I have been involved with training officers through the transition from revolvers to double action autos and then to the "safe action", striker fired autos. I can tell you from experience that it is far easier to train people, in a limited time-frame, with the striker fired pistols than it is with a traditional double action pistol. This, in my opinion, is why so many law enforcement agencies rely on Glocks and other similar designs. In the training arena, KISS is the best answer, ALWAYS.