The dot is mounted to a bracket that comes from a small picatinny mounted underneath that comes up the side and over the slider so the dot does not move.
The holographic dot is a cheap one that I got for an air pistol that I had a couple of years ago. So far it has been faultless for over 1k shots. Only thing I have found is the zero tends to shift a bit but not because of the sight but the bracket if handled a bit rough. I could not get on with the standard open sights and I am not sure if the target rear adjustable version will fit with the bracket fitted.
I think I paid £35 for the holographic sight and although not marked I think it was made by NCStar.
My only wish would be for a lighter trigger pull.