In my experience there is no full stop if zipper merge is done right, but lots of angry people and a an inefficient use of the road leading to traffic jam miles before the merge needs to happen if people try to get into the one lane early.

If people all zip merge, there is no zooming possible on the closed lane and both lanes that merge get down to around 20mph at the choke point.

This only works in countries with civilized traffic participants as mentioned by OP. I have personally only seen 2 countries out of maybe 30 where that was the case. In cars many people behave like animals for some reason