For those carrying Glocks and use an AIWB holster (me), the Tau Development Group SCD really is a nice add-on. I just recently made the move to putting one on all three of the Glocks I rotate between. Now, I have been carrying Glocks in this fashion for a while now and did not have the need for the SCD back then nor do I have one now, but after giving one a shot, it is really is convenient and reassuring to me. I like it. When re-holstering in general, I always put my thumb on the slide's back plate. Now that same action is a functional aid in providing one additional layer of safety when re-holstering.
I always appreciated DA/SA pistols/revolvers where you can place your thumb behind the hammer when re-holstering. The Walther P99AS had a firing pin that could be felt from the hole in its back plate if the trigger was unintentionally being actuated. Unfortunately for me, I have small hands and have trouble confidently reaching the DA trigger of these fine pistols, especially with gloves on during the winter.
With the Glock and SCD I get the exact feature I appreciated from the DA/SA pistols, but with a consistent trigger pull.
I went from carrying at the 4 to AIWBing and I do not see myself going back. AIWB really shines in the car or when sitting. I also find it easier to inconspicuously draw than when trying to do the same using the 4.
To each their own, just keep on carrying regardless, and with one in the chamber.