I won the CT laser in the last raffle. Put it on my wife's LC9 and have dry fire practiced it at home. It hasn't been to the range yet.
It lights up as you establish your grip and doesn't interfere with it. You do not need to establish a sight picture to see if you've got your target. I'd never want to shoot in an awkward or off-balance position, but it helps to feel things out if that became a necessity.
I really like it as a practice tool, but I don't want to build a dependence on using it and I do not have a holster that accommodates the LC9 with the CT. So for me, it's a practice tool. On or off in a SD situation would be irrelevant. The holster? That 's a bit of a game changer for me.