I kill more ducks with IC. I have to pass up some longer shots, but hit a higher percentage of the shots I do take with IC rather than Modified. Steel tends to pattern about one choke tighter than lead so I'm actually getting close to Modified patterns with the IC tube in.
I wouldn't buy a 24" barrel as a primary waterfowl gun, but you can do pretty well with it. I actually prefer 26" as an all around length and consider 28" to be pretty much for long range pass shooting only. Given a choice between 24" and 28", I'd pick 24".
You'll find it a bit of a disadvantage on long range passing shots, but an advantage on closer range quick snap shots or when hunting in flooded timber. It depends a lot on where, and how you hunt.