I've got guys in my rifle company that is currently deployed running on KAC BUIS right now as a primary day sights because their SDO or RCO broke and went WIR and we don't have a replacement yet from the depot. We already ran out of stocks to issue out as replacements.
I know this is in a .mil duty setting but.... Well..... we break everything... This is the same reason I laugh when people talk about the durability of AGOG's.... yes they are, and everything else would probably have broken too.... But Marines can destroy anything they are issued.... In ways you would never think of. So for us redundancy is a good thing and why I force my company to spend the time zeroing the BUIS.
My personal rifles all have BUIS on them because I bought a bunch back in the day and now they are paid for.... All my optics are on QD mounts or I have the tools on the rifle to remove the mount ( or tighten it up more likely). Haven't needed any of them in a while but they aren't in the way.
The night fighting SBR's I've compromised on, the rears are not a problem but in order to put the lights and lasers in optimal locations the front buis are located well to the rear on the rail. It is the fourth option though as both guns have IR and VIS lasers and then the XPS3's to fail before I have to resort to the irons. The pistol will probably come out first...to solve the immediate problem.