@Madbowh After carrying every version of a Colt M-16, almost daily, during just under 25 years of active duty, I always said I'd never own one. They just no longer held the same appeal to me as to someone who had never fired one much. Lesson #1 - NEVER SAY NEVER! Well, about seven years ago I bought a stripped down DPMS on a Black Friday sale at Academy Sports for $225 - yeah, that's right, a complete AR rifle for $225. I bought this specifically with the intention of buying a 22 Nosler upper receiver for it, but before I got around to doing that, the .224 Valkyrie came out. Somehow or another, this rifle began to breed because I now have five of them, in various calibers, on top of all my bolt guns.
I have one flattop Del-Ton that has the typical MagPul flip up sights, but forward of the rear sight I mounted a Sig Sauer Romeo 5 red dot sight. The two separate sight systems are set up in such a manner that I can use the red dot sight out to a couple of hundred yards. However, should the 2032 battery in that sight die, all I have to do is flip open the rear and front sights and I'm still in business. I can see the front sight through the red dot with no problems, so I don't have to try to look "under" it because they are on the same plane. Unlike the rifles from the 1970s and 1980s with the large see through rings, that is actually what is meant by "co-witness".
My Mag-Pul flip up sights are zeroed for 100 yards but requires a bit finer aiming than does the red dot. Either way, I have it set up to where I can put rounds on target out to a few hundred yards without changing anything at all.
My advice is to get a decent red dot with the high rise adapter and keep the A2 upper you already have. Before mounting the red dot, zero our basic "iron" sights. The mount you red dot forward of the rear sight and zero it. You can make minor adjustments until you can use either sight for any given distance within reason. This will also save you a bit of money and you'll get the best of both worlds without having to buy another upper receiver and change over from everything you already have.