I have a department issued Glock 21SF with an "old school" X200. I purchased a X300 and I run it with a DG-11 switch. In my opinion, I believe having a DG switch has many more advantages than disadvantages. Or at least the advantages outweigh the disadvantages.
In my experience having the DG switch during a building search gives you a HUGE tactical advantage. The DG switch leaves your weak hand open to do various tasks (i.e. opening/propping doors, turning on lights, cue radio mic, giving directions, etc.). If you did not have the DG switch, turning on the X300 with the rear switch is cumbersome and takes your focus away from the threat(s).
Some cons would be you need to practice NOT turning on the light while having your master grip. There is a high chance of turning on light as you unholster your firearm. Both technically can give your position away.
All in all, I believe having a Surefire weapon light with a DG switch gives you a tactical advantage. I trust this setup so much that I have purchased Surefire weaponlights and DG switches fo all my firearms.