Buy once, cry once - Trijicon RMR Type 2 3.25 MOA Red Dot Sight

Best red dot you can get. Little exspensive but they hold their value. Had mine for over a year and put a couple thousand rounds through it mounted on a glock slide(not frame mounted). A its still holding its original zero from when I first installed it. Yea the window frame is a little thick compare to others but thats to absorb the impact if dropped. This thing was made to go to war and back. Even though mine will probably never see any battlefield. It's a peace of mind having the best and knowing it WILL work everytime. or until the battery dies. Overall a decent asset to have. It hurt my wallet at the time but I'm happy. I can always sell it and get most of my money back. Look at it more as an investment.