I prefer the old fashioned method when transferring my photos to a computer, but I can see advantages to having your photos transfer to your phone when you're out somewhere and need to get your pics to someone ASAP and may be miles from your computer or a wifi connection. I first heard of them from news photographers who could now crop, edit and caption their shots on their iPhone and send them in from the location and not have to get to a Starbucks or steal an open signal from someone's unsecured router (more common than you'd think). And when Mom & Dad can't make it to the kid's recital, or the cousin's wedding they sure love it when they can see the photo right away instead of the next morning. Camera to Phone to Family.
I don't have a lot of use for them, but if I managed to snag one on sale I would, just for that reason. Don't know how many times I've been in the woods and snagged something cool that I wanted to share with the wife at home. Stick this in the second slot of my D600 and I could shoot the jpg copy off to her ASAP.