The big detriment I see to using barrel mounted apertures is that one loses the long sight radius gained by having the aperture back close to the eye, and loss of a lot of the subconscious self-centering of the front sight in the aperture conducted when the aperture is back right in front of the eyeball.* To each his own, and I'll admit they may be somewhat better than the traditional open notch barrel sight, but I choose to not partake.
Looking at the problem of mounting an aperture sight on a Browning/Miroku tangless single shot, I've toyed with the idea of fabricating a custom tang sight. Traditional methods are out obviously, but a sight base could be made that straddles the back end of the receiver with two mounting screws that are perpendicular to the centerline instead of on the centerline. Sort of like the old Weaver N-type scope bases of long ago. Another approach along the same lines could be an adaptation of the old Lyman and Marble's tang sights for use on Remington M12's and 14's - sights whose bases straddled the back end of a tangless receiver, with an extension that laid back over the wood that supported the sight mechanism/staff. Just thinking out loud, but a handy machinist could execute it.
Generations ago, when guys were employing custom target guns and hunting rifles based on obsolete falling block single shots like High Walls, Martinis, and Stevens etc., it was common to see flat bottomed receiver sights screwed to the sides of flat receiver walls, as far back as possible. Lyman and others marketed sight models for that purpose, and even the late/current Lyman 66 intended for use on Winchester/Marlin lever guns could be applied because they're of the same principle, I bet.
Of course one has to consider the modern propensity for abhorring the drilling/tapping of non-factory screw holes in rifles - a mindset I don't understand.
*Not to mention the advantage of a small aperture, right in front of the eye, for light focusing/sharpening front sight and target imagery.
