I have used a lot of wire strippers. When I first saw this type of wire stripper, I was skeptical, because every type of auto-stripper I had used before would work sort of, but seemed like they were more hassle than they were worth. They would either only work well with a small window of wire sizes, or they would need constant adjusting between wire sizess.
These on the other hand work with almost every common kind of wire. They work very quickly one handed, and rarely need readjusting.
They can strip small gauge solid core, small gauge stranded, and they can even help take the sheave off of Romax wire and then strip the individual conductors without any re-adjusting. They can even strip multiple wires at once, like speaker wire!
I have found these to be a large time-saver when doing a lot of electrical work.
You can also use them to open up the insulation in the middle of a wire without breaking the strands. This is a handy way to tap into a circuit, like in automotive applications. After wrapping, you just need to solder the joint and tape it. An advantage to this method is that you are not adding any internal resistance to the original wire, like you would if you cut it and then splice it back together.