I think that the Dark Urge originated from the tadpole thing. The more you used its powers, the less control you'd have over your actions, and ultimately, you'd transform. Now, with the DU origin, that'd make these elements overlap. Instead they went with the "tadpole tree" instead.
Personally, I'd have preferred the former version. You could play evil, use the tadpole and become more and more erratic, barely clinging to your sanity at some point.
For the custom origin, I'd have done a different story altogether. Maybe not even an absolute evil one, maybe an antihero arc with a chance of redemption.
But it is what it is, and I still don't use the tadpoles.
