Overall, the English translation of the Ajin manga is quite good. It keeps the core of the story intact and the characters' personalities come through. Some technical terms or cultural references might be a bit tricky to translate perfectly, but it doesn't greatly affect the understanding.
The 'Ajin: Demi-Human' manga stands out for its unique take on the supernatural. It has a well-paced narrative and the character development is compelling. The world-building is also quite impressive, creating a immersive experience for readers.
It's hard to say for sure. The decision often depends on various factors like the popularity and sales of the original series, as well as the author's plans and the publisher's strategy.