I've got nothing against folktales, but I'm really tired of how many Korean books for foreign learners rely on folktales for reading material. There's just not a lot of useful vocab. there and after a while I've tired of those green tree frogs and the tigers and the dried persimmons...
Hahahah! --yeah-- haha-- and I think I have discovered the reason politics have been so messed up throughout Korean history -- it seems that many of their great kings were hatched from eggs that dropped from heaven -- so that means they were aliens I guess
The book you found appears to have a very rich table of contents. It looks like worthy material but I think perhaps a little 답답한게 보여요.
I would like to suggest 3-5th grade elementary level book series designed for Korean children, not for foreigners. This I would say equals approximately high intermediate to advanced levels for foreigners. Here are a couple of the series I have found fun to read and or very useful:
어린이 과학형사대 CSI --do a search for this on your fav search engine - fun to read and very useful vocabulary (primary school kids using basic science to solve crimes) not comic book style -- just enough pictures to get the story across - somewhat conversational
신문이 보이고 뉴스가 들리는
30 volumes --hopefully the link works but if not plug that Hangul into Naver search - not really that much fun to read (pain in the @$$ sometimes) but if you really really want to be fluent in Korean this series covers much of the subject matter and vocabulary commonly in the news and topics of daily Korean conversations. I will be reading most of these books 2-3 times