Make sure you read the State restrictions on the site. Surprisingly, they are not illegal or restricted in California. Of course there's also pepper spray, but depending on the heat of the moment and wind, it can come around to you. Also, think hornet spray that shoots far, but in big bulky cans. The Knuckle Blaster easily fits in the pocket or purse.
Yes, I know the best defense is a handgun, but you probably don't want to use that in a simple scuffle.
I personally think this product could be used effectively and relatively quiet in a loud mob situation. There are other stun guns on the site, I prefer this one because of ease of use and being extremely difficult to wrestle away or knocked away from the owner. Of course, it you want distance, then think Tazer...but large and difficult to conceal.