The Gatekeeper incororates varistor surge supression. If they take a sufficiently big surge, they'll clamp the voltage, and sacrifice themselves in the process (*poof*). In actual practice however, I've had some varistor-type supressors in continuous service for close to a decade, in an area which experiences a lot of lightning activity. So far, knock on wood, I haven't seen one fail.
The particular ferite material that Ron's using for filtering in the Gatekeeper is pretty interesting stuff, and has a more profound effect on the sonics than you might expect if you've used ordinary ferite beads and various clamp on filters. Not cheap though.
