A good red dot sight is as good an investment as an A3 owner can make,IMHO
Having said that, I don't have a top of the line dots on my AR's(BSA on my M4gery BM and a Panorama Japanese make with multi reticles on my AR pistol/ MP-AR), but at close to $200, and coming with four reticle patterns, I love it...
The BSA is a basic 4 moa dot and if you use the top of the dot as your aiming point, I can get good results out to 80 yds with 12oz pop cans.
The Panorama sight is my favorite and resides on my Pistol build...
It has a simple and very fast 1 moa dot that would conceiveably work as well but faster than irons.
A 4 moa dot, ringed with a largerZ(don't know the moa though)circle around it like the EOTECH. This reticle is awesome fast at 50-75 yards, and you simply have to try it and see for yourself.
A set of cross hairs, with what appears to be about a HALF MOA dot at the center! Which is what I zeroed with. Not fast as the other reticles but more precise,as it seemed to work about as well as a scope,only no magnification.
Last, it has a 1 moa dot in the center, with a ring around it(smaller/more fine, than the 4 moa ring though), with a set of cross hairs that reach half way into the circle, pointing to the 1 moa dot
. This one seems to be the best balance of the speed of the red dots, with the accuracy of a scope. It basicly centers itself and you just squeeze off a shot... If done without moving, you hit what you see. I shot a five shot group that had one flier and all others were within a 1 inch circle at 50 yrd, off the bench of course...
I think everyone has already discussed the pros(super fast, reasonably accurate out to distances you cans see, and BOTH EYES OPEN SHOOTING) cons(use batteries, add more to a rifle, and not a substitute for irons, but a supplament) of the red dot, so I say, take the plunge if the bug is bitting, but shop around
...