Ghost rings are great for shooting at longer distances (+25 yards). They are great for slugs, too. I left the bead sights on my 870 since if I need it, I'll be using 00 buckshot at "social distances." At under 25 yards, bead sights are slightly faster than ghost rings.
I think Brookstexas was asking about PISTOL ghost rings. Aperture sights work differently on a pistol than they do on a long gun. On a long gun, the rear aperture is close enough to the eye that it "ghosts out". One's eye automatically centers the front sight in the center of the aperture...because the light is the strongest there.
On pistols, the rear sight is farther from the eye and, even when one focuses on the front sight, the rear aperture stays in relatively clear focus and doesn't "ghost out". One still pretty much automatically centers the front sight in the rear aperture.
To confuse matters further, Gary Paul Johnson designed a so-called "ghost ring" pistol sight, which is produced by Novak, which is not an aperture sight at all. It simply has a big semi-circular notch. It works just like all conventional "post-in-notch" pistol sights, but allows fast acquisition of the sight picture due to the "openness" of the "notch". I've tried this sight and, personally, I find it a bit imprecise and not any faster than a more conventional set-up.
If it matters, full aperture pistol sights are not legal for IDPA. The Novak "ghost" sight is okay for IDPA.
If they were really that good, every swinging Richard who shoots IPSC would be using them. I tried them for three months on an IPSC game gun. Fast, but not accurate at all past eight yards or so. To get the accuracy at distance, you had to slow way up. The pros didn’t outweigh the cons. Bad memories, very bad.