I think the offset iron sights are being looked at from a narrow point of view. Remove "back up" from the lexicon and look at them more as an auxiliary sighting system that can be used in lieu of or supplemental to the primary optic.
You can get fixed or folding versions, I prefer folding but if you think about it, traditional folding sights aren't much use either while they're stowed and to use them you need to remove the optic. With offset sights though you can just flip them up when needed, rotate the gun, and let it eat. There's no need to remove the primary optic, which also makes zeroing both systems much more simplified in the long run. In so far as them getting damaged goes, anything you strap to the gun can get damaged one or another but I don't think it's really any more susceptible to it. Some offsets, like the Magpul version, lock up on a ball detent so that if they get hit hard enough they collapse back down. The quality fixed offset sights are very robust and probably not prone to failure.
In a competition environment, which is where I use my offsets now, this lets me keep my primary optic on a higher magnification for long shots and use the offsets for close in. Depending on the stage this can save me from engaging close targets on 1X and then taking the time to swing the cat tail up to a higher mag, find my targets, and engage. Using offsets combined with a magnified optic also keeps me in Tac Optics and out of Open class at some matches.
As far as speed goes, I haven't compared them to an offset red dot but they're not exactly slow either.
