As with Randy, unless the square notch is huge, I see fuzzy sides. With a wide sqare notch, you have to centre the front blade carefully - too carefully. With a V notch, the bottom of the "V" helps with the centering. As the eyes get progressively worse, the best sight I've found is a wide "V" like on an English Express rifle, coupled with a bead front sight. No, it isn't only a close range sight only as some unknowing shooters and/or writers would have you believe. Even my old eyes, which appreciate that type of sight, are able to put 5 shots into 1 1/2" at 100 yards with just such a sight. The bead settles into the crotch and sits there, not moving one way or the other - as if it welds itself there untill after the shot breaks. Too, much of the animal or target is still visible to the shooter. The English still use it - from mid 1800's or so until now - must be useable, eh.
Perhaps the only style sight that is better, is a peep sight with bead or post front, but - they aren't allowed in "open sight' contests. An all-round sight should be useable in competition as well as hunting. There, the Express-type sight and a bead front sight is the best of both worlds and able to cross-over, doing outstanding work in both.
My eyes were opened to a different type of sight after the last postal chunk match held through this site. That is a square sided knoth, with a perfectly round bottom. The bead front sight is held in the bottom as it if was a peap sight. it is accurate and I am going to make a set for the .45 cal. barrel, just for testing. I've already got the front bead on the rifle, only need to make a rear sight - easy pickins. Any rear sight could be modified to this system - just need a front of the correct height - that could be the stickler. The sight must be the correct height to get the proper elevation for whatever zero a person wants. If the front sight is made a bit high, this won't be a problem as the rear can be filed at the range while sighting in.