These cards are pretty awesome since they are basically free card draw. They filter two mana into two different colours (which is pretty rare in and of itself) and they replace themselves at the same time. The best part? You can run all of these in the same deck! Since all the activation/cast costs involved are colourless, you can use the mana from one to activate another, creating a chain of cracking and drawing. Finally, these cards have some of my favourite flavour text in the entire game (Watnik is a boss). I don't actually have any complaints about these cards. They're pretty great for what they do. I don't know why they get so much hatred. It's 3 mana for 2 mana and a card at instant-speed. There's not much that can duplicate that.
Pros: Instant-speed card draw, dual mana filtration
Cons: Requires two mana to sack, single use