Over the course of my fairly long time (48 years) with shooting animals with irons sights, I've come to prefer a wide V and small bead for small targets and a larger bead for big game. I didn't discover this type of sighting for myself, until 1986 and I have preferred it ever since.
: A peep with ivory bead works well for bush country hunting. Rear V, square and U notch sights with posts are common on the offhand rifles I've used a lot, as in muzzleloading rifles, but I've come to prefer a wide V due to my aging eye sight. The narrow V, U and square notches fuzz badly for me to see easily and therefore my preference to the wide V. It's top surface fuzzes much less and the bead settles into the bottom nicley, giving good definition. The bead is sharp. I've been able to consistantly shoot into 1-1/2" with a round ball rifle with this sight system at 100 meters, 5 shot groups, so the sights work - for me at least. With the same type of sights, my bro has shot 3 1/2" offhand groups at 100 meters for 5 shots using a .50 cal longrifle of his manufacture, so they work for him too. His current hunting rifle, a .60 cal. 'Steutzen' Rifle also has a wide V and bead front sight. Seems people who give these Express-type sights a good test, like them. I've used them all, and the Express Sights work the best for me. These are the sights that allowed me to pull off 1/2" benched groups at 50 meters with my current longrifle in .40 cal. as well as with it's spare .45 barrel. Recently, I tested a square notch rear sight with a post front sight and the groups opened to 1" and 1-1/2" with both elevation and windage flyers for at least 2 shots per group. This isn't good enough as this is also my chunk gun for the coming season. If it won't hold 1/2", it's not good enough and only the wide V and bead give that to me.
: In my opinion, both our militaries have never used this type of sights as they aren't tough enough for a battle gun - certianly the front peep would be suseptable to damage. Mass produced peeps with protected posts of major size makes more sense for select fire guns. Too, I'll bet they've never tried Express sights. Along with this, a peep and post are much easier to teach non-shooters to use and the peep with either post or bead is more accurate yet, than any notched sight. This is also why peeps are not allowed in the BP matches I attend - esily aligned rear sight - it's automatic. I've used my AJ Parker rear aperature sight with both posts and aperatures up front on my match rifle and with good light conditions for the post, both are 1/2" to 1" groupers at 100 meters, shot prone. The front aperature is the most accurate, which is why many silhouete BP shooters use them for their animal targets, even though the animals are far from round.
: The Express Sight is back on my longrifle - it's accurate, easy to see and makes me competitive, whereas the notch sights are too difficult to see.