I suppose it depends on the keys, the flat blade works well on the BS keyboards(those keyboards are tanks). I don't think I would try it on my HHKB though.....
well, then again, I am reckless, I was able to pry the right Fn key off. But the flat blade is less than optimal for that purpose. The paper clip method sounds like it would be safer.
Though on the BS keyboard the flat blade works fine for me....