I put Ashley/Big Dot sights on my glock 23 a year ago, but was never happy with the accuracy past 7 yards (the rear sight is a shallow 'V' like an express rifle sight), though they are very fast at 5 yds. (which is kind of a moot point, since thats within index firing range).
Anyway, last week I put on a Novak halfmoon rear and got to test them at the range today. By putting the center of the dot in the middle of the circle formed by the half moon I got much better results. A-zone head shot on an IPSC target we no problem with about .5 to .7s split transition from 2 to 3 shots to COM.
I did not have time to go further out, but I'drecommend the setup, particularly if you have problems picking up a traditional front sight.