I assume you're talking about the dot in the screen type of sight...that said, I've a cpl of objections to them, ie...weight, bulk, and reliability.
For a carry type of defensive revolver or pistol, weight and bulk are of importance. Many will carry only so long as it's convenient and does not demand complicated clothing changes to accommodate. My wife is a case in point...she's got little patience for carrying when it's not convenient.
Reliability is another factor...how do they hold up to the sweat they'd be exposed to in normal hot weather carry conditions. Too, are they immune to a dunking...rain etc. It's the battery that's important here, as well as the screen to some extent I would guess.
Simple is good in defensive situations...the military has an old axiom...you'll fight like you train; and simple beats complicated nearly every time. You can train to use the dot but the learning curve to include the above objections/drawbacks may be steeper than some would allow.
That said, my wife has confidence and is quite competent with her Crimson Trace grip mounted laser, and it's improved her longer range accuracy 100%. She doesn't carry on a regular basis so the sight is mostly used for across the bedroom dim light situations in the 10 to 25 foot range. It doesn't make up for iron sights, but does give a quantum leap in dim light accuracy. The CT laser for us is a better choice...
Regards, Rodfac