I'm planning on concealed carrying an S&W Shield Plus, but going back and forth on whether to get it set up with an optic. Presumably, concealed carry distances won't require it, but given the short sight radius and stresses in a self defense situation, it may give you a crucial fraction of a second advantage. What's the conventional wisdom on this?

RDS have advantages and disadvantages.

For me, with my eyes getting older, I now have difficulty seeing iron sights with my daily prescription lenses. I use progressives, and have to tilt my head way back to use the lower part of the lens to see the sights with any clarity at all. An RDS solves that problem because you should always be target focused with an RDS.

The disadvantage is that you need to have a really good index when you raise the gun to be able to find the dot repeatably. Iron sights are much more forgiving in that regard because the front sight is easily located even if your index is poor. The front sight is always out there somewhere in sight, whereas if you are indexing an RDS badly, the dot is nowhere to be seen until you correct it to the point that the dot is in the window at all. I have seen countless people at matches draw their gun and then spend a couple of seconds fishing around trying to find the dot before they could engage their first target - the fraction of a second advantage you mentioned gets used up really fast!

My advice is stick with irons, if that is what you are used to and you can see them without difficulty. If you are well practiced in finding your dot from a draw with an RDS, the target focus is beneficial should you find yourself in a fight.

I switched to an RDS on my carry gun last year, but I was also using the same platform in regular IDPA and USPSA matches (2-3 times per month) so I was getting a good number of reps of drawing and finding that dot even without dedicated practice.

I’m the opposite.

I say put a red dot on your carry pistol. Take a few training classes from a qualified and reputable instructor and put in the practice and dry fire work to be consistent.

IMO - RDS is better than irons in the must fundamental way: You only have to look at a single visual focal plane - your target - vs lining up three focal planes (target, rear sight, front sight) like you do with irons.

Ultimately, irons or dots is a very personal preference. Just be comfortable with whichever you do choose.

My main point was that you need to be more diligent with your practice if you choose a red dot. It is much less forgiving if you don't have a good index.

If you practice to the point of unconscious competence, it doesn't matter - either is just a sighting system. You can be very effective using target focus with iron sights too - that's what all the hot guys in competition are doing these days. My eyes are just so bad now that I just see a very fuzzy outline of the back of the gun when target focused so the RDS is definitely better for me.

I have found that the red dot is more forgiving than irons when life is busy and I neglect training.

I can not shoot for a longer time and have less degradation of my skills. That being said, I do have 20 years of serious shooting with iron sight guns as a foundation before moving to learning red dots - so is it the training base? Or the new tech?

Who’s to say?…. Sample of one and all that.

Regardless, we should all strive to achieve unconscious competence no matter what sighting system we choose. We can be comfortable in the conscience competence zone as a maintenance minimum, but we should always work to level up.

An interesting experiment could be if you shoot a Glock predominantly, try switching to a non-glock with a dot and see if you find the dot as easily - or vice versa if you predominantly shoot a non-glock. The grip angle of a Glock is pretty much unique and demands a different index compared with most other guns.

I would posit that you adapt more quickly with iron sights on the first iterations.

I have a 3.3" micro 9 with RDS.  I use Holosun 507k with ACSS RDS from Primary Arms.  This has a very large outer circle with a dot in the middle.  You do not see the circle if you are on target, only the red dot.  If you don't have it aimed right, the circle lets you quickly and easily find the dot to get it on target.  No hunting for the red dot.    

Holosun HS507K-X2 Compact Pistol Red Dot Sight - Red ACSS® Vulcan® Dot Reticle (primaryarms.com)