I have an SD 40 (same as the 9mm except for caliber) and two Sigmas (which the SD is based on..pretty much the same gun), one 9mm and one .40.
Things to keep in mind:
The gun does not have a manual safety, but it is a safe gun.
Don't obsess about the stiff trigger or "change it out" like 70% of Sigma or SD owners. The stiff trigger IS the safety. I shoot my Sigma about as accurately as my other dozen other 9mm's.
Since it doesn't have a safety, it needs to be carried in a proper holster that covers the trigger guard.
Unlike many other full size pistols, I can carry mine IWB, but it ISN'T the optimum CCW weapon. Better choices out there.
Most importantly, don't let the gun snobs do their psychology on you. They will trash SD's. I also own Kimber, CZ, Walther, etc 9mm's. The SD, as a self defense tool, will function as well as the rest.
Best wishes.