I confess I’ve always disliked DRS (taking the Wacky Races argument) but I think there’s are valid arguments that if you’re going to have them then more are better than fewer.
For one, it means that anyone who’s firmly out of position can get back more easily, so anyone taking engine penalties or suffering a botched pit stop doesn’t have their race ruined quite so much.
But more compellingly it means that if you have two drivers racing closely, if one passes the other a bit too easily under DRS then they may become vulnerable at the next zone. At one or two tracks drivers have occasionally used this, choosing not to pass in the first zone and instead doing it in the second so that they can pull away before becoming DRS prey themselves.
I think as a stopgap until 2021 it’s a reasonable tactic. If Brawn’s claims of reducing following-car downforce losses from 50% to 5% are accurate then DRS’s days are certainly numbered.