Tried one on a Remington 597 22LR rifle and I was surprised at how well it works. For rifle functionality I'd place it between regular open sights and a good set of aperture sights, certainly not as useful as a scope. I have plans to try it on a Ruger 22LR target pistol, but haven't got there yet.
I have the original square model with the original delta reticle, SeeAll was selling them at half price probably because they were changing over to the new delta and cross hair reticles. Since these are limited in range by your eyesight, I think they will work better on a handgun than a rifle. My handgun experiment is probably a fall/winter project.... but I'll try to update this thread.
My purpose for it would be a 7.5 inch 556 ar budget build I just finished. No intentions of trying to reach out past 50 yards. Might give one a try too.