I tried very hard to like this sight - Meprolight M21 1x30mm Reflex Red Dot Sight and Fubs Self-Illuminated Flip Backup Sight

Good things: holds zero, durable construction, great reticle, easy to range, easy to zero, good glass, no batteries.
Not so good things: reticle can disappear in certain conditions.

The best example I can give is shooting this on a range at 4pm in the afternoon facing away from the sun under a lean to. In these conditions, the reticle all but disappears against a solid black silhouette target at 100 yards. I even bought the aftermarket REM21 illuminator that is powered by a CR2032 battery. This fires LED light directly into the light collector and has 11 settings of brightness. There were just instances in low light that the reticle just disappeared and made the sight basically useless.