I have been shopping for a front sight and chose the Troy folding m4 buis. The hk sight only works well if you can adjust the rear sight for elevation. Moving the post up and down misaligns the circle in circle sight picture as real hk firearms use a fixed front post.I hope that helps!
The front post IS elevation adjustable but when moved up and down it is no longer center of the "circle in circle" sight picture. To use them properly you need a rear sight with adjustable elevation and fixed front post like hk firearms use. The KAC are also a great choice likely going on my next build