Aperture sights are iron sights. I find them to be faster and more accurate than u-notch rears. I have a few guns with aperture rears...10/22, Saiga 12, K31, Marlin 512, 870, Sub2K, SU-16... only the two KelTecs came with them stock.
The smaller peep openings can be a bit troublesome to use in dim lighting, otherwise, I love them. If sticking with iron sights, they're the way to go.