My replaced my AK's U-notch rear sight with one that has a peep sight (more like a ghost ring). It works a lot better than a U-notch when it comes to sight alignment and sight picture. Much faster sight alignment and more accurate.
Thats a matter of opinion I suppose.
I tried the Mojo's when they first came out on a couple of guns, and quickly found them lacking for any kind of realistic use. The peep being so far from the eye, still requires you to align the sights, something your eye does naturally with a true peep, and with it forward, there is really no reference for zero, like you get with the leaf using a traditional sight picture. Low light, and bright light from behind, like the sun over your shoulder, just aggravates the problems more (low light from behind is also an issue with a traditional peep). I had the same problems with peeps on a pistol, and for the same reasons.
I find the AK's issue sights to work very well, and are actually quicker to use, even over a "real" peep, especially up close. Even at longer distances, they are more than adequate for reasonably precise shooting. In that respect, the Mepros actually reduce the guns effective range, due to the front sight being so wide. The Springfield SOCOM's also have that issue, but even more so, as their front sights are even wider.