Well "chatter" is when your switch fails to debounce properly. By definition, it can't happen on a switch that doesn't have any contacts to bounce in the first place.
Of course, there are various ways that different kinds of non-contact switches can go wrong, but none of these would count as chatter.
Could you clue me into what kind of things can go wrong? I haven't read about any potential issues with Topre or its clones. Only good things.
Also, should I interpret your answer as "Yes, all EC switch keyboards, Topre or otherwise, are chatter-free"? Sorry to press the point, but it's the main reason I'm considering a clone at the moment.
Right, any keyboard without contacts, which includes Topre and its clones, cannot experience chatter.
The clone boards aren't exactly running the World's Cleanest PCBs, which can cause random issues. If you read the comments on the Royal Kludge boards from Massdrop, you'll see that people have experienced issues with stuck keys, missed keystrokes, and even ghosting. Mine suffered some ghosting-- this went away after I gave the PCB a thorough going over to remove crud and residue left over from manufacturing, but I wasn't able to get the dome sheet off without damaging it, leading to more problems down the line.
I should point out that there are a couple of options besides EC switch keyboards if you want to avoid chatter. As I mentioned above, it is logically impossible for any switch without contacts to experience chatter. This includes not only EC switches, but also optical switches (e.g. Flaretech, Light Strike), which are available in a variety of characteristics, and magnetic switches (e.g. oldschool Hall Effect, the fancy version of PadTech's switch), which are usually linear.
Alternatively, if you want a lower-tech solution that doesn't require you to break out the soldering iron all the time, you can look into keyboards that support hot swapping switches-- there are a bunch of different ones available now. That way, if a switch starts to chatter, you can just pull it out and put in a new one.