CNET did not review the DirecTV HR21 but we did review the HR20, which is very similar.
Although CNET did not review the DirecTV HR21, we did review the HR20. The two DirecTV satellite DVRs are basically identical aside from coloration (the HR21 is black while the HR20 is silver) and the fact that the HR21 lacks a built-in ATSC tuner, so it cannot receive or record over-the-air HDTV channels. The HR21 lacks such a tuner, although many local HD channels--typically ABC, CBS, Fox, and NBC--are available via satellite in most areas of the country (more info).
The HR20 and the HR21 share the same capacity for recorded shows, the same remote control, and the same features otherwise. For more information, refer to our full review of the DirecTV HR20.