I have had experience with sigmas. Some will run fine and some will be plagued with malfunctions. They shoot ok if you can get used to the horribly heavy trigger. Sometimes,you really can't put a price on a gun for defense. What I tell EVERYBODY is to get the best possible handgun that not only fits,but that you can actually shoot well. This means going to a range and renting several guns after you've narrowed it down a bit from natural fit.
If you can afford a better gun then go for it. Whatever you decide to go with,as long as it's reliable and you shoot it well,that's great.