I'm not arguing that feral bonds are the right/wrong answer, I'm arguing that it's a minor point with no real answer. While in the long run it has a chance get you more money faster for your rainbow, not all elements players want to do that. And as it's a life mono deck, the person who'd play it would probably want some life gain, as that is life's real point.
So I guess what I'm trying to say is:
If you're simply making this deck to zip ahead for a rainbow, don't put the EBs in.
If you're doing this for fun, because you like the element life, or if you have no plans to make a rainbow:
Put in the EBs.