My experience with two rear sights on a changeable rear sight

 For a changeable rear sight. which can be changed almost instantly. 

Personal.

Rear sight which is rectangle with a small rectangle groove, and round and | on the front.

-I use this one with normal light.

-Better accuracy maybe.

Round rear sight, quit big. And a round front sight, with a |

-I use this one with lower amounts of light.

-Easier to aim and faster. More to see, and more light comes trough.