I can remember when the first purses with pistol pockets came out. I really felt sorry for the ladies because they looked more like something you'd carry carpenter tools in than female stuff. Fortunately, manufacturers got serious about the project and quickly came up with more fashionable bags that might actually appeal to a lady.
Since those days, men's shoulder bags have also made an appearance. And, while they might not be all the style in Horsethief, N.M., the cosmopolitan gentleman has the same option as the ladies for carrying his defensive handgun.
Bags with a designated pistol pocket are most valuable because they allow a person to carry a larger, service-size handgun when he/she might not otherwise be able to. Just about everyone does his best shooting with a larger handgun but, especially in warmer climates, there may be quite a number of months when it is simply not practical to try to conceal it on the person.
Always keep in mind that it is really not a bag; it is another kind of holster with a loaded gun in it.
In addition, the defensive bag makes carrying extra ammunition extremely easy. And the defensive shooter also has room to carry some sort of less-than-lethal defensive tool if so inclined. With the variety of bags available today, the defensive shooter can pick and choose to find one that is serviceable as well as fashionable.
One of the real advantages to carrying in a bag or purse is the fact that it completely conceals the defensive handgun. One doesn't have to worry about someone seeing the firearm and getting all upset. It virtually eliminates the question of brandishment in those states where that is part of the concealed carry law. 
However, as with any other carry mode, there are drawbacks to carrying the defensive handgun in a purse or bag. The first is that a person might be the victim of a purse snatcher instead of an armed attacker. When one of these crafty folks makes off with your bag, he becomes armed and you aren't. One might argue that this is the reason for carrying the bag with the strap in the across-body mode because it makes it more difficult for someone to grab. People who adhere to this theory have simply never seen a purse snatcher at work. Ask any veteran big-city cop about purse snatchers and you'll soon realize that if the purse snatcher can see the bag, he can get it. And he'll get it quicker than you can stop him. Another problem with purse/bag carry is the tendency for a person to lay it down while tending to other business. At the point that you lay the bag down and are no longer able to reach out and touch it, you have lost control of your defensive handgun. And, of course, the problem is compounded when you get forgetful and walk off and leave it.
The final issue that I find with bag carry is that a proper pistol presentation takes much longer than if the gun were secured in a waistband holster and it takes two hands to access the firearm. When time is of the essence—and, believe me, when you are being attacked, time is critical—the presentation will be slow and especially so if you only have one hand to use while you fight the attacker off with the other. Getting a gun out of something that is swinging from your shoulder is not conducive to a quick draw by any stretch of the imagination.
In the final analysis, I can't tell you if purse/bag carry is good or bad. That is something that you have to decide for yourself. It is my hope you will do that after making an honest assessment of your own personal defensive needs. Be conscious of its advantages and its shortcomings. And always keep in mind that it is really not a bag; it is another kind of holster with a loaded gun in it. With that mind set, decide if it will work for you.
