This is one of S&W's most thoughtful designs, and its features fit its intended market perfectly. I'm selling them like pancakes.
The market is people (mostly women over 50) who are not expert handgun shots, and who may have compromised hand strength due to many factors. This is a growing demographic, consisting mostly of very nice people who are awakened to the need for personal defense.
The features that work great for such a customer are:
1. The .380 cartridge in a relatively large, heavy pistol (compared to the pocket guns: LCP, BG380, Micro and 238) is easy to shoot with minimal recoil, while with good-quality hollowpoints has more than adequate terminal ballistics. The barrel, which is longer than those in the pocket pistols, adds a little to velocity for better performance in the target. I recommend Hornady Critical Defense loads for this pistol.
2. The mass of the slide permits a very light recoil spring which makes it easy to operate the slide.
3. Beginners often insist on an external safety. Even if you and I don't think it's necessary, it gives them peace of mind which is, to them, a real benefit. The grip safety is the best kind for this owner, as it does not require a deliberate movement to deactivate, a movement which the owner might forget in the supercharged atmosphere of a real DGU situation.
4. The pistol is equally easy to field-strip for cleaning. These owners want to know that they can care for their pistols themselves.
5. The knobs on the magazine follower make it easy to load. If it still presents an issue, I recommend a Baby Lula for loading.
Many of these people were (wrongly) told that they have to settle for a revolver due to inability to rack the slide on other pistols. But a revolver or double-action pistol is a terrible answer for someone who has hand strength issues due to its very heavy trigger pull. I had a customer who traded in an LCP, because she couldn't pull the trigger on it. The five-round capacity of a carry revolver may be inadequate in a multiple-assailant situation.
As far as a 9mm version goes, it would make no sense. Anyone who can handle the recoil of a 9mm easily will also be able to operate the slide on a 9mm Shield, which is smaller and thinner, ergo superior for IWB or pocket carry.