Superb sighting system - Meprolight M21 Self-Powered Day & Night Reflex Sight w/ Dust Covers

I am very pleased with the Meprolight M21!
I ordered the triangle reticle version, and the sight has exceeded my expectations. The reticle is very crisp, with no distortion in a wide range of lighting conditions. It magnifies much more clearly than LED powered reflex sights, and the triangle reticle provides a precise aiming point. The optic is also 100% waterproof; despite having an open-emitter design, the emitter location is recessed into an enclosure, in front of which is a drainage channel. I recently used this sight in heavy rain for an hour, and never lost my reticle. The lens is tinted blue, which cuts down on glare on bright days.

The biggest con to the sight is washout - the reticle can fade out against bright weapon-lights, or when shooting from a dark location into a bright one. Co-witnessed iron sights, or the polarizer attachment is a must if used at night. I purchased the polarizer, and the sight is now usable with my 1000 lumen WML. The robust construction adds weight (14.2 oz), and the sight displays some vertical parallax in the top 1/4 of the lens.