FWIW, I found that the reading glasses move the plane of focus too close to do work with my hands. You can slide them down your nose only so far. By having the magnifier further away, the focus is also further away. (like the giraffe system) I've been meaning to try one of these types of movable magnifying glass systems, but have been hesitant to spend the money.
The only problem with the head strap that I've found is that it looks goofy, but hey, I'm tying with dead animal stuff on a hook that's too small to see, what do I care.