Very nice to have.
I purchased the test device as well. I was shocked that one outlet in a room (w/ a computer) read 1800 & this plug reduced it to a reading of 32. It works immediately. For anyone suffering from dirty electricity, these are worth having. Make sure to buy the (sold separately) test device meter to go w/ it. A lot of readings were above 300, so you might need more than 1 set of 4 filters.
Rating: 5 stars