Tl;dr Don't read unless you've finished the story and its a great read for those who have.
Personally I am really enjoying this manga. It contains major spoilers to the rising of the shield hero because it takes place right aftermajor events in the main story. Therefore all his knowledge contains those spoilers as the remembers it. This ties in very nicely with the story and to say it is a spin off is actually incorrect, but rather story that is taking place between his death and when he returns to fight on... For those that have read ahead in the story you know what I'm talking about and you'll enjoy the change in pace.
Okay now to the execution
The personality of Motoyasu is very true to his character and it really pulls off how sick in the head he is and honestly I find the humor from him more funny than in the original story. The story gives more details about Silt Welt which was never really visited in the original story and some of the alternative turns of events are quite interesting. The story also fills in the gaps as to what happens to Motoyasu after he died and what the spear offered him upon death. For someone who's read the WN it really fills in an itch and I'm interested in seeing how events unfold.
The art work is once again the artwork is well done and I really have no complains.
Character development: 8
Due to the change in environment and having not facing as many hardships, many of the MCs have a more lighthearted approach to things and are developing differently than they did in the main story. Motoyasu remains the same in his undying love towards Filo, but there is a growing bond between him and the other characters that's quite enjoyable to see.