While researching my reply I found a pretty good thread on this at dslreports from a couple of years ago: thread

Any such things worth the money will not rely on isolating the house but rather grounding the incoming power (they'll disconnect the house too, but the key strategy is to dump the incoming voltage/power spike to ground). They'll go between the meter and the circuit breaker box, often right next to the meter (since it's easier to install the ground cable outside than at the breaker box).

The most important part to look for is a huge cable or spike going straight down into the ground from the whole-house protector. This is the most important part and must be installed right. If a unit doesn't make big deal about the ground cable, leave it on the shelf. The rated lengths of this is in *inches*, not feet, so if some yo-yo wants to put the box in a convenient place and run a long ground cable somewhere else, hire a different yo-yo.