I've have two, one on my main key ring, and another on key ring with assorted, small back up gear, such as a Classic, P-38, Fenix E01, and something else, in a box under the bed. I like them quite a bit, and much better than any other one piece tool I've owned.
Since my three year old has developed the habit of locking the door of whatever room he's in, the one on my main key ring is frequently pressed into service to unlock doors. Every single interior door in my house can be unlocked with a slotted driver. And while carrying a SAK makes carrying the 4-way driver redundant, I also don't always carry a SAK.
Its other main purpose is acting as a metal thumbnail, primarily for the tabs on soda cans.