I'm glad everyone is having fun hacking the firmware via the RS-232 port, but back to basics for a bit...
Though this box is undoubtedly worth the 18 bucks PP I paid for it (after coupon), like almost every electronic item from China (where apparently engineering and attention to detail don't seem to be a priority), I've observed a number of flaws in the design:
1) The aforementioned zoom issue is a little more complicated than previously stated. If "zoom" is selected on an HD subchannel, it does the right thing. If "zoom" is selected on an SD subchannel, it either: a) has no effect at all if the SD mode is 528x480i or 640x480i (which is the desired effect and would be wonderful if not for b), or b) stretches the picture horizontally (off the screen at the ends) but not vertically (a purely nonsensical effect) if the SD mode is 704x480i; SD subchannels in 704x480i seem to far outnumber the others, but here in Philly there are some of both (for example 10.2, WCAU's weather channel, is unmodified by "zoom", as are all the WPPX/ION 61.*).
2) On my unit, at least, the NTSC video output leans toward the left at the upper right hand side. Normally, you wouldn't notice this on an SD channel, or on an HD channel showing widescreen content. But on an HD channel showing 4:3 content (or on telecasts with some vertical object or a vertical edge on the right side of the screen) the lean very obvious, as it is when displaying the menu; it's as if the upper NTSC scan lines are shorter and more compressed than the lower ones - some kind of analog distortion. No, it's not my set... I've tried it on several. May be a sample defect, or may be intrinsic to the design.
3) One OTA channel in the NJ/Philly area scans in with the wrong subchannel number (WMCN-DT, which PSIPs as 44.1 on any normal DTV, comes up as 44.3 on the Tivax, with no 44.1 or 44.2 at all.) Fortunately, this station shows automobile advertisements all day long, and is virtually worthless anyway.
4) After a power failure, the unit DOES remember what channel it was last tuned to. BUT, if it was in the "standby" state prior to the power failure, it comes up in "on" state after power is restored. That is, it can remember the last channel, but not whether it was on or off!
5) The "standby" and "mute" buttons on the remote are positionally reversed compared to virtually every other (i.e. Japanese) remote. Power is almost always the upper right button on a remote, and if colored, almost always (for whatever reason) green; on the Tivax green-top-right is mute. Bizarre.
6) The overscan in all aspect ratios is excessive, chopping off useful portions of program material, like the tops of heads and scrolling news at the bottom of 4:3 and zoomed 16:9 pictures- much more so than any typical NTSC tuner.
7) This unit's tolerance of varying multipath (i.e. trees blowing in the wind) is rather mediocre. I think a lot of folks who buy CECBs are going to be pulling their hair out because of this issue, which is by far the most significant problem with ATSC reception in the suburbs.
So like most Chinese stuff, decently manufactured but poorly engineered and/or tested. My $.02.