I don't know which Red dot to buy I'm thinking either the aimpoint m2 or the ml2 I also like trijicon thought they are way out of my price range.

What is the big difference with the m2 and the ml2. I was told the m2 was for use with night vision is this true?

My understanding is that the M2 is used by the military and has a few settings for night vision.  The ML2 is exactly the same without the provision for night vision.  If your order the M2 be sure to pick one up for me too

I have been looking into the Reflex M21 as a possible red dot for a 16" AR carbine. The Sportsman's Guide has them for $299.97 per unit. That seems to be a good price.

In the description, they list them as not requiring any batteries...as in daylight the sight uses fiberoptics to provide the dot and tritium at night. It has a 5 1/2 M.O.A. aiming point. The unit weighs in at 14 oz and is described as being very tough and rugged. It is fully adjustable for windage and elevation and comes with a built in Weaver type mount.

This looks like the red dot for me. If anyone can provide any additional info, please do so. And if anyone is interested in this sight, do a search for item # HX2A-61583 over at the SG website.