Couple thoughts here.
First is that a 9mm out of a short rifle or a .223 with proper ammo will not overpenetrate more than a 12ga. with buck shot. Those misconseptions were dispelled during the 90's but still pop up. Most SRT's use .223, or 9mm +P+ primarily with one 12ga, mostly as a door lock buster.
Any of the above options beats a handgun for self defense, stops for a .223 is around 97% way better than even a .357 which is one of the best. Also longer guns are easier to point and shoot acurately under stress, fire rapidly and retain without getting shot with it, if you use a good sling.
Short shotguns almost always have short magazine tubes, main downside that caused SRT's to move from SG's on to SMG's and AR's is increased capacity. I can't imagine being happy about a four or five shot weapon. A very kick butt seargent once told me, you can forget most of thee kit, but pack all the socks and ammo you can carry on the run.
If you are buying a handgun buy what you shoot accurately, noting else matters.
My wife is the best shot with a Sig 239 I dragged home to refinish and resell. It's hers now, I don't shoot it well. I like the Glocks, a custom compact 45 officers I built and a Para Limited, she hates them all. We both shoot a S&W 66 I have very well, and neither shoot a S&W 432 she bought well at all.
At the end of the day a cartridge will destroy a few ounces of flesh, which few ounces far outways, gun brands or cartridge balistics.
opeyes: I wanted something I knew I could put a few shots out without getting to shaky. If I could i would get a 40 cal. 
