I sincerely hate this form of "behaviors", simply because you lose all the useful stuff coming from ProfileElement. Subclassing ProfileElement lets you have full-blown XML element support (which also ensures XML validity against required custom tags).
It also enforces some certain documentation (such as author, etc) that is incredibly helpful to everyone.
Secondly, you can subclass from QuestProfileElement to get access to some quest-related API (specific to quest tags).