TFX Pro- Remington sight.  Patridge sight picture and low light illumination.  Easy replacement for factory open sights.
The rear sight is sufficiently wide for a quick sight picture.

https://www.truglo.com/firearms-tactical/tfx-pro-remington-shotgun-sights.asp?catid=85782AB719C042A394366B7DDEB2FF93

For what it's worth, I have found that rifled slugs generally group tighter from barrels with a chamber length that matches the shell length.  Jumping a quarter inch gap seems to distort foster slug designs.   

I think you may be correct about the slugs.  I've never had a gun that really excelled at grouping the Foster type slugs from a smooth bore - better luck with the Brenneke style in terms of accuracy out of my guns.  Neither is particularly accurate for me at a hundred yards but that is a lot to ask from a non-rifled barrel and a projectile with all the aerodynamic efficiency of a badminton shuttlecock. 

I understand that it is a tritium/fiber optic combo sight but I wonder, have you tried it outdoors or in the woods at dusk?   There is a time of day when it is hard to see an illuminated sight because its not exactly dark and also hard to see a light pipe type of sight because its not exactly light either.  Any experience with that kind of thing?   

I agree with you re: the ghost ring set-up.  I tried a home defense rig once with that type of rear sight and it was a humbling experience.  Not good at all in some environments.  Since then I have come to prefer either a dot on a post type sight picture or a dot on a dot like the Heinie Straight 8 style pistol sights on a traditional iron sighted gun.   For me the jury is still out on the red dot/reflex/holographic sights on a heavy recoiling self defense shotgun.  I like the quickness they provide in sight acquisition but electro-mechanical devices are prone to failures not common with iron sights. 

For hunting situations I like your selection as well as any. 

Yup.  If it isn't projected to sell enough units to justify the costs of the production run its not looked upon favorably by the bean counters.