Tried one and did not like it. It's really only usable with a flat shooting gun setup, or with an adjustable rib/comb setup. I did try the Meadow Industries sight. It is similar but the top of the tube is open so you can use it with sight pictures that show more rib than a figure-8. Yes, it helped, but did not cure. I found green better than red for trap.
They work in the sense that you can not see the bead with the non shooting eye. But you will get the guys on here telling you "I took a shooting clinic and they told me to black out the bead don't use it". If cross dominance is your problem it may or may not help. But your other eye won't be seeing the bead.
I know these clinics are great and taking a few will help anyone. But all of the things that work for the instructor will not necessarily work for you.
Some say the bead is too bright and it is a real bright dot to be sure. But it helps me.
I think if conditions are such that the bead is brighter than the bird, that's a negative. It may draw attention away from the bird and cause a bit of bead checking...a surefire way to stop/slow the gun.
Most people that I know that have tried it use it for a while then take it off. I bought 2 guns that had one in the case.
I have had good results with the EasyHit sight on my 686 SP hunting 20 ga. I prefer Meadow Industries Vari-Brite-Site II/III for my trap guns. As mentioned this fiber-optic sight has a channel rather than a tube. Trouble is if you lift your head when you are not suppose to you still can see the bead.
I like the orange bead. I want it as obvious as possible. My thinking is that with the front sight glowing out there, there is no need to look for it.
I shot one with good results until I was caught in a light rain during a shoot-off, the "pipe" fills with rain blocking the optics causing total blackout, same deal at night under lights. Being such a long sight it really cuts down on the sight plane or optical distance that a 34" barrel provides.