https://www.creedmoorsports.com/product/gehmann-eyecup-for-standard-1-inch-disc-or-iris/-Gehmann https://www.nordicmarksman.com/Anti-Glare-Tube-6700-20.html Champions Choice has these rubber cup also
some people think they are worth 30 bucks when they can be had for 10 bucks or so
and as casual shooters we have no damn rules use what will help you enjoy the sport
i will say that if you go to the trouble to buy a Gehmann diopter and not get at least a Gehmann 510 iris you have missed the boat
and if you would try the glare tube on the front of the diopter you will see a different look
we as shooter like many different things and agree and disagree use what works for you, diopter sights and there counter pair the globe front sight are not cheap by any means and your homework is wise to do and to understand all of the differences and the similarities
now Mike D and i have had more post together on this subject over the years, we are both hoarders of sights and bit and pieces and the question would be why and the answer is we can
the diopter globe sight rabbit hole is a big one jump in and educate yourself i for one at the age of 73 is at the end of my life and we as hobbist need someone to educate the younger men and women about all things and one is sights
take care guys have a great turkey day
mike in Washington