It really feels like a rather pointless product given the current state of HVAC manufacturing. Until HVAC manufacturers make zone control more of a priority paired with having technicians that are capable of installing it properly.

Between all the environmental and construction related variables it would seem that it would take a 3rd party to develop something that could integrate with the various residential systems you can have installed with a reasonable warranty attached. Without having a bunch of automated dampers, properly insulated homes/duct work it seems a bit premature to try and market this as a product that makes sense for the average human.

Can someone explain to me what these actually do? Doesn't there need to be a way to actually manipulate the airflow into each room (air vent flap motor etc)?

That was, partially, explained part way through the article:

These sensors make the whole system more accurate and keep things comfortable. That might come at the cost of overheating another area of your home that you’re not in, though. Unless you’ve got smart vents, heating systems are nowhere near precise enough to set different climates for each room.

So basically for heating this is a "min temp" sensor per room. For cooling I assume "max temp".

That's what I read as implied by the quote from the article.