The best replacement for iron sights is scope.

The best alternatives to iron sights are rated as following:
★★★★★  scope
★★★★  optics
★★★★  red dot
★★  aimpoint
★  optics ar-15
★  eotech
★  peep sights
★  scope ar15
★  holographic
  open sights
  optical sights
  scopes
  with scope

Your alternative for iron sights is not listed? Suggest!
Speaking about iron sights, one probably shouldn't forget about acog.

Other search terms related to iron sights and their ratings are:
★★★★★ acog
★★★★ eotech
★★★ red dot
★★★ magnifier
★★★ scope
★★ optics
★ aimpoint
★ both eyes open
★ scope ar
★ shooting
You have in mind a companion for iron sights and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of iron sights in all years. Click on graph for more.
iron sights
scope
optics