Extractor pliers grab on to nails, staples, and brads even if the head has been clipped off — or was damaged when you tried to remove them with conventional hammers or prybars — then provide leverage (via a curved head) to allow you to pull the fastener cleanly.
The idea is that as you push the handle down to rotate the fastener out, you’re also pushing the jaws closed, so you put a lot of force on the fastener without putting too much force on whatever the fastener is stuck to.
We’ve had pretty good experiences with these, removing finish nails from custom molding and trim without damage or from the front or back-side.
But the real question here is: does anyone really need a $25 pair of nail puller pliers when there are locking pliers and prybars around? Let us know what you think in comments.