The "Clear TV" antenna (2 for 19.99) actually is 2 for $35.93 when you add "processing and handling". You can get a similar (RCA) antenna at Wal-Mart for for under $17. The are two problems with either antenna. The first is that it is an un-amplified indoor antenna and will work about as well as a set of rabbit ears. It will pick-up signals at 15 to 30 miles from the transmitter, assuming that you don't have a lot of buildings/trees between you and the tower.
There are also similar indoor antennas with amplifiers. These extend the reception radius, but not significantly. Your best bet is a big old Yagi antenna mounted on a tall mast with an amplifier and rotor. [We had one of these back in the 1960's so we could watch the Browns games out of Columbus; they were blacked-out in Cleveland.] No matter how "digital" TVs get, they still live off good-old radio waves.
If you have a decent, open location and spend a few hundred bucks, you can get a fair amount of broadcast TV, including the HD signals.
HOWEVER, after consulting the Metrocast Basic channel line-up, I can tell you that you will not receive any channel that is not included in what you already get. You will definitely lose NECN, 3 home shopping channels, 2 CSPAN channels and 3 "education and government" channels.
To get any "good" channels, you will need to bump up to Metrocast's "Expanded Basic" service. None of these can be watched via an antenna, although some may be available over the Internet.
Instead of an buying an antenna, you might consider "renting" one from Aereo (
https://aereo.com). Depending on how their Supreme Court case comes out, you can rent a small antenna + DVR (physically located in Boston) and then watch all the "local" stations over the Internet (about $9 /month). This won't be an improvement over Metrocast's Basic service, but it is cheaper.