For PK you have two primary capabilities as a armadillo. 1) Is as you said, getting the fuck out is easy as a armadillo. You can pretty much guarantee survival. 2) In group vs group combat its a clutch form, it can continually intercept and spam the skill over and over without any lag. Its a group vs group combat CLUTCH form.

For MOB killing you have a few uses. 1) You can get through many areas that have tons of aggro mobs all positioned in adjacent rooms. Think draconian tower or mausoleum as good examples of how it can get through areas like that with relative ease. 2) Create distance/revert/ca slow/sleep, shape dillo, repeat. That's how you use any non-regen form. Its straightforward, really.