I have been experimenting with RDSs for pistols, target and defense (daylight and low-light). I have nothing negative to say about them. They increase the capabilities of those who are already capable. Unfortunately, the comparisons to rifle RDSs just aren’t there, that being, a decrease in the learning-cycle of aiming. If I could make one recommendation for an upgrade to a pistol for defense, it would be a WML. Then a RDS, and then night-sights. For target shooting, whatever floats your boat.
The ability to positively identify a potential threat and control their visual horizon (WML), outweighs the advantage of a RDS for 90% of the people I see at the range. But RDSs are an advantage to those who are already skillful. I think taking a 2-day defensive pistol class would do more long-term good than buying a RDS.
I fully support RDS-mounted pistolcraft, but for 90% of people, in 90% of defensive situations, they are almost irrelevant. I use them, and they’re wonderful, but realistic expectations of our own capabilities should precede throwing money at a problem. Unless of course you consider me a problem, then throw away.