Iron sights work all the time, optics and points will fog over/get wet/get dirty/get covered in snow....
If anything of this happens to your irons, just spit at them and wipe them. If anything breaks the irons, optics will be dead long ago.
-> I like iron sights, but use mostly optics. Optics just help to see the target better, they don't make the rifle more accurate.
My BUIS is a Troy folding aperture sight and the 71b ARMS frontsight.
I use mostly a surplus Fero Z24 scope with my M5.
This fall I shot with the BUIS from 0 to 600 meter. From 0 to 300 with a 250m zero, from then on at a 450m zero.
The Troy works like a charm. Crisp sight picture, reliable and sturdy.
With the larger aperture I could hit poppers up to 200m very reliable. After finding my POA I could hit the poppers consistently at 600m with about 50% of my shots (small aperture)
The single negative point is the absence of elevation adjustment at the aperture.
Therefore I will try a KAC 600m sight to see if it works for me.
Shooting at 600m with the Fero Z24 scope was nearly boring, I was able to hit with more than 80% of the shots. Prone supported, prone unsupported but stabilised with a vtac sling and prone unsupported. Most misses were unsupported.
Good times.....