Yes, you may use the converter box in place. The only down side is that you will no longer be able to watch cable TV. You will be able to get up to about 44 channels of regular TV on these boxes.
Pro: no more fees
Con: no more cable
Depending on what TV you have, Flat screen v. the bulky older version, you may also need to buy an antenna.
If you own a flat screen, then you may not need a converter box. Just the antenna.