There are both good and bad CDM-831 units, and you're far more likely to run into the bad than not (ie, black AVT-8710 performance). This model was released right around the time that production supplies changed to the bad Cypress chips that causing freezing and frame sticking (and other issues). To date, I think I've only ever seen one 831TR that was good.
I know that several are/were still being sold new from a supplier in New Zealand, but I've already confirmed those are bad units. I've mostly seen it for sale "down under" (Australia, New Zealand), and sometimes imported/used in some Asian locations.
This was a PAL-native unit, and the NTSC performance is generally bad (but not always, maybe 1 out of 10 times?). The PSU didn't seem to like 110V in most cases, probably a QC issue in R&D where it wasn't well vetted (ie design flaw) -- not surprising, given the chipset failings.
The default values were also off, and needed tweaking. That can be hard to do when you're new to this kind of gear.
I've been seeking TBC alternatives for years. Found some good options, found many more failures.