Alright. I just gave this one a go. Do take this review with a grain of salt as this is my first review on the website (and probably my last). I'm not gonna talk about the characters as Tsubaki is just Eren and Murakamo is just Mikasa. This is a prototype after all.
Story 6/10: The story's the exact same as AOT, titan shifters, titans, inner walls, ect. There's some tweaks here and there though, such as the titan's weak spot being the nucleus, and the vanguard corps (survey corps) using katanas. The titans were also a human extermination operation by scientists and religious groups if I read it correctly.
Art 3/10: It was pretty bad...Isayama has come a long way. The entire one-shot just felt like a rough sketch. The art was comprehensible but it was terrible at the same time. In fact, the art is so bad it's actually quite funny.
Overall 4/10: If your a fan of AOT then check this out, it's cool to see the concepts Isayama planned before making the serialized version. It's also nice comparing his drawings from back then to now. Otherwise it just feels like a waste of time, your not gonna gain anything from reading this. That's all I gotta say.