I presume you mean the cocked striker indicator. I've been thinking about making one for my SR9. If nothing else the added mass would translate into more positive primer strikes. I'm not experiencing these, but the added benefit would be there nonetheless.
I have one in my SR45. It's purely cosmetic. Had I thought about it, I would have got the extended length one that pops slightly out when a round is chambered, so you can feel it without looking at it. More effort than it's worth really.