I purchased 2 APC surge protectors, one for landline telephone and one for ethernet. With zillions of dollars of equipment at home connected to landline telephone and ethernet, these devices provide some peace of mind. Although I have whole-house surge protectors, those don't guard the landline telephone or ethernet cables and the attached devices, so I consider these absolutely necessary. (I also have something like this for my cable TV, reviewed elsewhere).
After installing them, I noticed no degradation to either my landline telephone service or broadband speed. One of these days I will post photographs of my Data/Comm/TV distribution panel showing these devices. Please check back in about a month.