I would be curious to know what happens before this 5 day test. Do people just walk in with resume in hand and sit down to work for 5 days? Probably not. There would have to be some sort of discussions-that-aren't-an-interview which would lead to a yea-nay decision on the work term. What sort of funnel is there?
I agree there is a big commitment on both sides to do this 1-2 week work stage. There has to be more to the events leading up to the stage than what's in the article.
As it is with my current employer, it would be very hard to just take 5 days or even 3 days of for something like this, paid or not. If it was with a couple of months notice then I would think it wouldn't be a problem, but with shorter notice than that it would be hard.