"Whole house" surge protection.

You're probably safe to accept their offer; these devices are typically shunt-protection types so would not cause any series-current limiting or ground hum. Be aware that there are different models of primary arrestors. Carbon block types are really cheap & will mainly prevent a house from burning down, but that's about it. M.O.V.'s (metal oxide varistors) are very fast & clamp down transients to very low levels, although they're somewhat limited in current capacity for the lower cost models. Gas discharge tubes are the best: more costly, clamp down low, & can handle a lot more current & repetitive hits. I have an industrial grade Joslyn gas discharge primary arrestor across my main service inputs. I've heard it operate a few times when lightning hits closeby; it sounds like the "surge hum current" of a very large motor starting up. One hit was so big that the shunt current draw actually tripped out the main breaker on the utility pole's service disconnect. I still have additional MOV's: one across my dedicated line's outlet, as well as MOV's internal to the Chang Lightspeeds which also serve for AC noise filtration. Of course I recommend a Joslyn as the best level of protection, but anything is better than nothing at all.

Go to soundstage.com (archives or Reviewers Choice 2001) and read new review of Shunyata Hydra, at the end of review there is a discussion of surge protection and and installing electrical panel protectors.

There are two types of electrical surges that can be produced by lightning: directly injected and indirectly induced. Directly injected is that which enters on the power line and will cause a surge potector at the service entrance to fire. Indirectly induced is caused by the elecromagnetic radiation produced in the atmosphere by the lightning stroke. This electromagnetic radiation can couple to the house wiring and cause damage eventhough the primary surge protector across the service entrance does not fire. For this reason it is wise also to use MOVs or other protection devices at your equipment. If you have a large surge enter on the elecrical service, only having protection at the equipment itself may not be enough. So, to be really safe both are needed.

This is essentially what Bob_bundus has done in his house--primary protection at the service entrance and secondary protection at the equipment.