IMO, the only DACUS that's difficult to incorporate into a playstyle is Wolf's and Shiekf's. Wolf's is one'a the harder ones to do consistently, and there ain't much use for a DACUS U-smash anyways. Not 'less they're on a low platform or doin' somethin' stupid like charging a move close by, i.e. DK's Giant Punch.
Shiek's is the hardest DACUS in the game, real narrow timing. Ironically, I find it a lot easier than Wolf's.
... Don't mind our horribly nerdy Brawl discussion, InDarkness.
It is quite useful
I mastered wolfs but not fully shieks
and if you do falcos fast enough you can perform his dash attack into quick upsmash without the need of a buffer
Wolf's can catch people off guard once in a while
Sheiks's can be done out of a grab
Snake's is easy and very useful
Falco's is used for damage racking
It's an extra option, always good t' have. Wolf ain't too good on approach options as is after all. It just ain't too practical to use it if the stage isn't somethin' like FD. ... Well that, or when you're B-air WOPing and want to suddenly charge in. I ain't one to spam B-air for spacing, but on the rare occasion I do a well-timed DACUS definitely does catch some players off guard.
Using it effectively. It ain't DACUS as an AT overall that can be difficult to apply, that ain't true so long as Snake is legal. It's individual DACUS'.