I find it an unnecessary gimmick that leads to complications (some of them mentioned in the article), especially in countries that already have a considerable amount tightly regulated vacation days. (I.e., every Western country besides the US.). For instance the legal obligation to pay out remaining vacation days if someone leaves means you have agree on a number and keep track of them.

In practice, 25 days vacation (with the option to save at least some of them up over time) is more than enough for most people, and you'll be hard pressed getting most motivated workers to actually use them all up.

Especially if you are a decent employer that allows people to work from home if convenient and doesn't deduct vacation time for trivial matters.