Partially fills a niche but mounting options are few - Holosun HS407K Red Dot Sight

4 Stars because I'm willing to try it on my carry gun. 3 Stars would mean I refuse to try it. Overall, quite disappointed.

In design, the Holosun 407k has the cowitness, low profile, and narrow footprint features of Shield Sights along with ruggedness similar to prior Holosun optics, which approaches the ruggedness of the RMR.

In function, the window is smaller than an RMR, it lacks autobrightness, and the cowitness of the rear notch doesn't quite allow a decent view of the front sight (but you can see the top of the front sight, so it's better than nothing)

Mounting solutions are presently very frustrating. It uses a modified version of the Shield Sights footprint. Gun or mounting plate must not have rear lugs, and the front lugs need to be shorter than some of the normal Shield or Leupold lugs. In other words, no guarantee that it will fit your gun. I made it work on mine, but I'm still not sure if I will keep it.