I believe
@Metzos has already pointed out the total recovery frames on the grounded omega beam. About one third of characters in the game can crouch and whiff punish the grounded omega beam at mid range. Some examples include...
- Aquaman's FTD
- Atrocitus' blood puddle
- Deadshot's wrist shot
- Firestorm's mid flame carpet
- Flash's lighting punches
- Poison Ivy's vine drill
- Supergirl's trait
- Swamp Thing's close and mid vine grab
The instant aerial omega beam has a much superior recovery to the grounded version but cannot hit at certain ranges because of the arc. You will have to know at which range to use the grounded and aerial version and in which match up.