The problem is, when you are not picking the first taxi is, that the other drivers are not willing to drive you, because you "should" take the first taxi !!
I didn't have any problems when I have exercised my rights.
I've only done it twice: once I needed a station wagon taxi because there were several of us with quite a bit of luggage and once I didn't have any cash and didn't want to go to an ATM, so I picked the first taxi lined up that took credit cards.