Man that is one of the "kitchen sink" rear sight accessories.
Looks like diopter adjustment, iris diameter adjustment, different color filters, maybe a polarizing filter, and I don't know what else.
- iris diameter is used like the iris in your eye, the darker the range the larger the iris, the brighter the range the smaller the iris
- colored filters are for different light conditions (indoor, sunny, cloudy, etc), different colors are supposed to make the target easier to see, some people like them others don't
- polarizer, similar to a polarized sunglasses in effect
I have two of the simpler ones; one with just the iris adjustment, and one with iris and colored filters.
Since my shooting glasses is already yellow, I don't use the colored filters. Turns out my preferred adjustment for the iris is the same as the stock fixed diameter iris.