Best feature is aaa battery - SIG SAUER OPMOD Romeo5X 1x20mm 2 MOA Dot Compact Reflex Red Dot Sight

This is a simple inexpensive red dot. It doesn't have multiple reticles, just a red dot. The glass is ok. It mounts securely. The biggest benefit is using a AAA battery because they're cheap and abundant. There are fancier red dot optics with more features but this is simple and inexpensive.