Never used them but they sure look like they would eliminate the problems I have with the old style U notch and bead and should be quicker to use on running targets.
Who makes it?
That sight is made by Marble, they call it the Bullseye. I've never used one but like what they say about it. I'm considering getting one for one of my flintlocks as my older eyes don't work as will with the old irons as they used to. http://www.marblearms.com/rear-sights.html