I can see the benifit if you have a real load of holes to drill in one job, but I'm not in a mega rush to save 2 mins!
It's not just about time Andy, it's actually much easier to use a grinder.
There's no dust to speak of really.
But the real advantage is that your hand is very close to the actually drill bit, which means it's easier to control, a lot easier.
With a drill you need to be sure it's vertical and so on. Using a grinder your hand is just a couple inches away which is a lot easier and they are far more less likely to skate like a drill bit.
Trick is to slightly rock your hand in a circular motion and not just push straight down. This makes them far more efficient and increases the life 10 fold.