Falco's recovery is too short to even hit Marth's counter, duh! lolol trolling.
Anyways it's good if your positive it'll land which it should if they aren't Marth spacing an F-smash or something rangy like that.
If it misses, you're back to square one since you now have to Firebird back to the stage at a possibly even worse position than before. (You'll be charging right in front of the ledge which makes you vulnerable and in range to lots of crap.)
Or even if you hit them, and if they're too low percentage, they might not be knocked far enough for you to Firebird back on safely after your bair. Kind of like Falcon up+b you at low percents, but you still have time to run back and edgeguard.
EDIT: It's flashy and cool, but since you're Falco, just don't be cocky offstage. Just phantasm instantly and sweetspot the edge after a walltech to go for the safe option.