This is what I’m seeing, a lot of LPVOs with MRDS. I have one setup that way myself. My RDS guns have BUIS. Should have a least two minimum sighting methods IMO.
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I feel that for as small as some buis are there's no real downside to having them. I really like the MBUS pros.
I might use an RDS to backup a magnified optic on a range only gun, but anything intended for off-range use will have BUIS. I think I only have one AR that doesn't have BUIS and it hasn't even been to the range yet.
Modern optics are very reliable. That being said they do still fail. I drove to my uncles ranch in Oklahoma to do some hog hunting. My TA31 ACOG died during the smooth highway drive there. Sitting in a padded hard case too. Luckily the back up irons on the gun still worked.
On a more serious note, a dude in my company had his Aimpoint shot off his M16 in 2005. He flipped up his irons and continued the fight.
I still have standing irons in front and back of my red dot. Non folding. They aren't in the same plane of focus as the red dot and don't interfere with the red dot sight picture, I never even think about taking them off. They're just there when or if I need them.
I used to put folding back up Iron sights on everything. But you reach a point of accumulation where that no longer makes a lot of sense.
Around two years ago I switched from putting them on everything to as follows:
Scoped rifles - Scope only, no irons
RDS / EOTech - Optic and Irons
Then of course I have rifles with irons only and those that come with iron sights standard with some sort of optic added. EX: HK91 with claw mounted Hendsoldt Fero Z or MP5 with an RDS.
My oddest combination is the Tavor, it has an LPVO with a small RDS on top of the scope. It also has the built in folding irons as well.