I think random QD actually works a lot more than it should lol. Surprise tactics ftw.
I probably should've been more specific though. Such as, don't use QD when your opponent is at 0%, because even if you hit, he will be able to hit you back since the lag is so bad. Also, don't start charging QD when both of you are at a neutral position, especially if the stage has platforms (if it's FD and your opponent doesn't have a projectile, you might be able to get away with it).
I probably should've been more specific though. Such as, don't use QD when your opponent is at 0%, because even if you hit, he will be able to hit you back since the lag is so bad. Also, don't start charging QD when both of you are at a neutral position, especially if the stage has platforms (if it's FD and your opponent doesn't have a projectile, you might be able to get away with it).