I put a set on my Glock 27 and used them for about a year. As Bender said they are for fast target acquisition and not for tight groups. There is definitely a learning curve with these. I eventually changed them out for a set of Glock factory night sights since all my other guns have similar type sights. It was difficult for me to transition from the XS Big Dot sights back to the "traditional" sights on my 1911's and other handguns. They're a great site if your everyday carry is the same each and every day. Unfortunately I change everyday carry often depending on if I'm working, walking, or traveling. It was easier for me to change them out on one gun than to change several other to XS Big Dots.