As a certified instructor, I've trained with them and do provide information about them to my classes, but I must say it is a far less than optimal way to carry.
The only way a gun is going to be of use to anyone is if it is on their body when they need it. A purse in an office is going to be put into a drawer or locker. It will have to be locked securely.
Any kind of purse can be taken away from a woman rather easily, especially from behind. In a crowd, the mugger merely cuts the strap, so the method of carry of the purse is fairly irrelevant. A "fanny pack" is no more secure. The strap can be cut and the purse or pack snatched quickly, before you notice.
Most women put their purse down frequently, especially in the car. If you are separated from your purse, you will not have access to your gun and, most likely, no time to get it. You may also lose it to a thief. Then you have the pleasure of knowing that you just provided a firearm to a thief...
A lot of women are willing to live with these serious limitations because they don't believe they have other options.
I'd suggest they do some reading here at "Cornered Cat":
Cornered Cat | If you have to fight, fight like a cornered cat.
They might find some other answers.