ATI Theater 650 PRO appears to be a discontinued product and we have not tested it. However, we support most ATI products, and this one will most likely also work, especially the digital TV part (ATSC). The only sure way of finding out is to plug it in and try using it.
Since you do not subscribe to cable services, you will not have any use for its analog tuner (and since more and more cable companies goes digital, an analog tuner will have very limited use, unless you tune directly using the cable box provided by company). You can use the device for ATSC (over-the-air HD TV in North America).