I've been running MRDS on my pistols for over 2 years now. They excel at a number of things, but also have some cons.
Draw -- you do need to ensure you have a high presentation - basically I draw and elevate the level pistol right up in front of my face - then start my push/press out. This allows much faster acquisition of the dot -- after a few thousand reps, it is quicker to pick up than irons.
Rapid Strings of fire -- with the slide mounted MRDS, you will loose the dot under recoil, so you either end up slowing down to reacquire or slide indexing.
Accuracy - depending on your MRDS, and how you run the intensity, as well as distance shooting, some will see massive gains over irons, or a degradation. Inside 10m I find I am often not as precise with the MRDS guns, as I am with irons, but 10-200m I am much better with the MRDS.
Low Light - the MRDS is much easier to use
Moving (Shooter, Target, or Both) like a CCO on a carbine, all you need to do is put the dot on the target, I find it much more effective than irons.
GasMask -- MRDS kills irons, more doubly so in a smoke/gas filled structure.
NODS - MRDS is stupid easy to align thru ANVIS googles, I can shoot the same scores as my day quals at night wearing googles with a MRDS, times are a tad slower - but due to the view field in the ANVIS.
Shield Work -- the MRDS shines like a mo-fo if your LE using a Shield, I generally don't like Shields (they don't stop rifles), but for interior work domestically, they are pretty good (and some exterior situations) and the MRDS allows timely and accurate usage - unlike irons.
I run a MRDS on my Carry Gun, my BUG, and my SWAT pistol (which I also carry everyday).
These days many Mil SMU's are using (or giving options for) MRDS on their handguns, and a lot of the vanilla SOF units, and LE SWAT entities are doing it well.
As long as one understands the downsides, they are an exceptional tool.
Last comment -- ensure you use a slide milled for the MRDS, the dovetail mounts in addition to being higher and more awkward do not mount the MRDS securely into the slide, and cause premature failure due to the increased G load on the optic -- handgun slides have some nasty G loads, so you do not want to make it worse.