I have them on a few Ruger revolvers, this is the sight picture of my SBH Bisley Hunter 41. You really need the fiber optic (Marble's) front sight to get the most out out of it, IMHO.
They send two apertures, one is 7/32" and the other is 9/32", I prefer the larger one for quick target acquisition. I think I have a small aperture left over if you want to try it without risk. PM and we'll talk.
I will say that if you want to shoot a gnat off of a bulls ass @ 50 yards this system is not for you, but I found my groups closed in significantly and it is pin-point enough for 100 yard whiteys.