The elephant in the room is that when any of these pictured reflex sights/mounts are fitted, the shooter needs to lift his cheek some considerable distance off the comb to make the shot. Turns a perfectly fitted DR into a nightmare for fast instinctive shooting. Even introduces difficulty for precision shooting I would expect.

Principle is sound though, but I am still waiting for a truly low profile reflex sight to be mounted so the "dot" is at the same height as the standing leaf was.

The "window" need be quite small, as the cheek-weld will position the shooter's eye perfectly in a properly fitted double.

Seems to me all existing examples are designed for handguns, where there is no cheek-weld, and the gun can be brought into line no matter how high the sight-plane.

There was such a low-profile sight available about 35 years ago, pre-internet, but it didn't last and I can no longer find details. It was about 15mm wide and no more than 12mm high iirc, total! The two fellows in my shooting club who had these things back in the day have now passed on to their reward, so no details forthcoming from them I'm afraid.

Thought the Hex Wasp might have been a goer, but sadly bad reviews are far more prevalent than praise for that one.
Still waiting....

Sorry this turned into a bit of a rant, but I have been holding back on all the threads on this topic hoping for some enlightenment, but finding nothing to entice me to run out and spend.

Now, back to dot shape...!