Works for me. For me the main draw back is the cost of the sight. If Trijicon starts getting some competition that is as heavy duty as their RMR, then perhaps the prices would go down.
Big advantages to me:
My eyes aren't what they used to be. I have trouble focusing on irons, particularly with speed. With the red dot, you keep focus on the target, looking through the dot.
Iron sights are somewhat dependent upon sight radius for accuracy (i.e. most people shoot better with longer barrels). With a red dot, there is no sight radius, so barrel length is only relevant as far as bullet velocity.
Dots are very visible in most lighting conditions, though if you aim at a bright light, the dot will wash out.
The RMRs are extremely reliable, but in the event it should fail, back up irons are easy to transition to. Other red dots are not as sturdy. I have Burris Fast Fires that I use on a Ruger Mk III and a AA .22 conversion for my Glock. They work decent, but I would not rely on them on a self-defense weapon.
My RMR equipped G26 is no more difficult for me to carry concealed than the standard version. I carry either in the same position (IWB-appendix)
Would money spent on a red dot be better spent on ammo and/or training? Well, maybe, but you could say the same thing about money spent on that second (or 25th) handgun.
Do you NEED a red dot? Again, maybe not, but if you can afford it, why not? In my personal experience, I can shoot better with one than without one. I want every advantage I can get if I am forced to defend myself.