I have an Aimpoint H1 on my DA Grizzly. I have very poor eyesight with astigmatism. This causes the red dot to appear expanded/enlarged, and much bigger than the 4MOA dot it's supposed to be. Due to the erratic and uneven expanding, it's difficult for me to tell exactly where the center of the dot is.
Even with these astigmatism problems I still prefer to use the red dot. It's very fast to pick up in low light.