I went and checked around some Japanese reviews on why there are two mangas and what are the difference.
The gist of it is:
Nobody knows why there are two. The Authors and Publishers are keeping mum about it.
If you have read the LN before and just want to see quality art and expressions, go read the other one.
If you haven't read the LN before and wants to see an authentic recreation of the story, then go read this one. The raws for this one is actually more accurate and is further into the story than the other one.
That's about it.
Personally, even if you say that this one is more accurate and is further into the story, the fact that there is only 1 chapter translated means I'm probably putting this one on hold until it catches up with the other one or something.