It's parallax corrected, and it's also necessary since you aren't always looking at the dot from the same angle. The dot moves around so that it stays on the same spot (reasonably) on the target when you move your head around in relation to the sight.
Anyway, I have one similar to this (it was one of the brand name ones). They're decent reflex sights for the price. If you don't want to dish out a ton of money for an EOTech, this is a neat, cheapo alternative.
As for the vision bit, I've found it to be true for just about any dot sight (Aimpoint clones, Docter Sight, Bushnell red dot, ATN Ultra Sight and this model); if your eyesight isn't 20/20-ish (natural or corrected) the dot will be blurry.