I bought one a while back to see what all the hubbub was about, and while I like it I don't find that I use it a lot.
I don't have to pay for range time, so time isn't really and issue, and loading mags is the one activity where having gorilla fingers is actually useful.
So, it's not really anything that works for me.
However, if you're regularly in a rush, or have any trouble getting the last couple rounds in, they seem like they would be very handy. They definitely work better than the free ones that come with your gun.
si vis pacem para bellum