I recently purchased 2 CECBs, the Channelmaster CM7000 and Target's RCA STB7766G1 (which is like the Venturer STB7766G1 and Winegard RC-DT09 models.) I used a Gateway FPD2485W PC monitor that has NTSC S-Video and Composite inputs, which may show up more flaws than a normal TV.
Compared to RCA, The Channel Master's picture is cleaner and fine details on graphics are noticeably better, even using Composite. S-video was only a slight bit sharper. Reception was superior to the RCA on 2 channels (45 and 58 UHF) but worse on another (16 UHF), using the same antenna. Unit had Thomson tuner module inside. Remote awkward for simple surfing of channels, menus quirky. I think the engineers designed it without user trials. Closed caption has small font, can be adjusted however. "Subtitle" button should be CC for closed captions!
Compared to Channelmaster, The RCA picture had more jagged look, not as smooth on network logos, graphics. Color and contrast and sound were comparable on both boxes. RCA box has simpler small remote but I found it more convenient for regular surfing and menus are easier as well. Closed caption font larger, remote has CC button. I kept this box because I can use the Winegard battery holder RC-BP9V with it in a power outage.
CM wins for picture quality on a good SDTV set. RCA wins ease of use and unique ability to use in power failure.