These 'Were-cassowaries' are a great idea and worth exploring, but I think they need more polish, detail, and mechanical work. However, this little pdf is Pay What You Want, so the author isn't asking much.
I think that with additional work and detail, these could become a very solid addition to Werewolf: The Apocalypse. As they are, I like them but do have some thematic and mechanical concerns.
It's entirely plausible for Pentex to unleash these things on Australia. They're certainly an improvement over hypothetical dingo-based War Wolves, on a continent where wererhinos really won't work. Cassowaries are fierce and dangerous birds, and suitable stock for a Mockery Breed. The idea for how they turned towards Gaia is a good seed, and of all the Mockery Breeds they have the best chance of redemption. The name is also great - fitting and very 21st century. Overall, this is a great idea.
Thematically, the Murder Birds' redemption is too easy and complete for me. I think the Werewolf setting demands a much more arduous and unfinished path. Gaia immediately adopting a creation of Wyrm-industry and turning them into a full Changing-Breed without Wyrm-taint just isn't plausible to me - I think She would demand ages of service to Her before She'd bless and embrace them, if it's even possible. The mental realm they inhabit is a cool idea but would make more sense with an origin from a captured Mokole, rather than a Corax; a genuine Yathamaya would be a good explanation for learning about Gaia. Making their redemption and new allegiance an ongoing process, a path they have only started upon, would also create more possibilities for moral grey areas, conflict, and character/story development for Murder Bird PCs - or even for Gaian shapeshifters who want to help them.
Mechantically, I don't think it's plausible for them to have the full range of breeds and forms - no canon Mockery Breed has that, and I don't belive Pentex could pull that off. I'm not sure the powers are balanced, but they won't play in a mixed-Breed group, so maybe that doesn't matter.
Lastly, the layout isn't professional, and there's no artwork.
With all that said, Murder Birds are worth using for any Werewolf game in Australia, Papua/New Guinea, Nusa Tenggara, or Maluku, either as player characters or as a completely unexpected mystery (and moral conundrum) for any Changing-Breed. As antagonists or wild cards, you could throw them at any WoD splat (except wraiths) and enjoy the players' confusion.