As far a Killers go this has to be one of the best in the game, sadly however theirs no really amazing killer as they all come with a down side from Garrotes price tag to Ninjas poor Str and dagger is no exception. It requires stealth credits to gain that huge Str increase and has no Str to start so will need it just about all the time, This means adding Silencer, Cloak or Ghost Runner to the deck.
Still its one of the most efficient Killers requiring only a few creds and a stealth to break only Switchblade or Femme Fatale are more efficient and they both have their down sides in comparison to Dagger.
It's worth noting that it can be helped out other ways too, you can use Datasucker's, Dinosaurus, The Personal Touch or the new Net-Ready Eyes to help reduce the stealth requirement of Dagger. It's also worth noting that because of this Killer and alot of things are in Shaper to help it, it makes it so Shapers can have a full efficient rig without spending any influence. Using this one of their many decoders and Snowball / Cerberus "Lady" H1 makes for an effective rig. All in all a great Killer that takes some setup to get working but very good once it is.