I've nailed about...6 rats with a rat zapper.
The trickiest thing about it is baiting it with something that will lure them in. The instructions mention that rats tend to be somewhat leary of entering unfamiliar confined spaces and that one should give them a few "free meals" before activating it. Just pick something tasty and smelly...I think I used cookies, Hershey's Kisses, umm..I dunno, it's been a while since I nailed all of hte rats.
BAsically, you bait it, turn it on, and then go about your business.
Here at the house the dogs (german shorthair pointers) were going crazy trying to get into the crawl space under the house for a few weeks, and after finding turds in the kitchen and even seeing the furry bastards racing around the beams in the garage, so I bought one and tried it out. I'd set it each night before bed, then check it the next morning. AFter a couple of days it started getting them. It has a led light on top that blinks when it has discharged, so all you have to do is glance at it to see if you nailed something.
The main con about it is that they're pricey ($45 I think). The one I had stopped working so I bought another.
The biggest pro is that they're high on the "cool" factor, and very clean. Just pick up the trap, dump the carcass wherever you decide to dispose of it, and rearm. No blood or guts or any crap like that. Quick and humane, too, if you care about that sort of thing.