The dagger looks dull and far from dangerous. But appearances deceive, for this weapon has been imbued with a dangerous magic.
Like all daggers, the dagger of the double strike is better in situations with high tension. Its double strike ability will allow you to hit people more often, making it useful against enemies that rely on concentration. Because of its low damage output, you should not use it against enemies with high damage resistance, such as the ravenous armadillo or the wisps of pain.
While the -2 attack penalty may seem tough, remember that not only do you get a second strike, but your enemy will not be able to react to that second strike. On the negative side, you will no longer have your concentration bonus.