@UndulyUnruly Oh, you are right on the commuting part. I did not think about that.
Not so sure about the "time with family" argument, though. If I had to work 10h days I would not see my kids when I come home for 4 days. Now I see them every evening. Sure, on the other hand you get 3 WHOLE days to spend with them.
Guess it comes down to personal preference. :)
edit: But the idea behind the 4 day week after all is 4 x 8h, not 4x 10h. Because otherwise the productivity would not increase. And the article clearly states that this is the main goal.
Well, 4x10h are not more than 10h a day, right? And if it is 4x9,25h (37h week), then you even are able to do 0,75h overtime per day, still within the bounds of law. At least that was my understanding.