Given the size of the thing, I could see it being useful for emergencies. I mean, it won't come CLOSE to fully charging my phone, but it's easier to keep on hand than a full power bank.
This is only 1200mA. I just bought a 5000mA charger, just a bit larger than a lighter, for $17 including shipping. Sure the size makes it more convenient but what would this charge besides an e-cig or pocket flashlight?
It's almost half the capacity of my Nexus 5's battery, but I usually only occasionally need and extra hour or two so this should be very convenient. I have a large battery bracelet but I never remember to put the thing in my back pack.
I already carry around a 2200 mAh battery pack which is enough for a full charge of my iPhone 6 and is about the same size as a pack of butter menthols. If you can pick up a decent one for a decent price then as long as you remember to put it in your bag (Which is the appeal of this one as you can put it in your wallet/purse) then you will never run out of battery while you are out for a day again.