Speaking to the "need" for backup irons, it depends on the usage. Open division pistols don't run irons and shooters in that division (1) train to pick up the dot quickly and (2) generally run reliable red dot sights, reducing the likelihood of "needing" backup sights. If you're building a TacTimmy gun for slayin' goblins the "tactical" wisdom is to keep cowitnessed irons, but on a dedicated Carry Optics competition gun I think I'm OK without irons.
I'm seriously considering having my P09 set up for Carry Optics, and won't miss my irons. I'll just have to train to the dot, not unlike if I were moving from Limited to Open.