I have not tried using a red dot type sight on a rifle, I have them on my Bullseye Pistols, but I am only shooting out to 50 yards. At least at 50 yards, with a handgun, I cannot hold hard enough to evaluate parallax sighting errors. I will say, I absolutely center the dot in the field of view before firing. I center the post in my irons, and I center the reticle in the scope. I found that off axis sight alignment creates off axis shot placement.
You should be close enough to go to CMP Talladega and ask the Range Officer's what they think about red dots on rifles. One of the Range Masters at Talladega told me of an red dot type manufacturer that brought out sights with long guns and could not group worth a hoot at distance with the things. It probably has to do with centering the dot in the field of view. I think for the Mall Ninja's and "Tactical" types, these sights are just great for shooting at 25 yards or less, quick sight acquisition and of course, these guys love to rock and roll. At the range you will hear them burning off 20 round magazines in seconds.