Bonniers did print at least print one reading book in 1966 with the title "Prins valiant och konsum" (Prince Valiant and the Cooperative). There are no pictures in this book and it's written by P.C. Jersild.

The story presents one of Jersildt's favorite themes: something absurd happens on an ordinary day and changes everything upside-down. PRINCE VALIANT OCH KONSUM (1966) is about a girl's dreams of a comic-book hero in the monotony of a Swedish grocery store.

Small A5 size book. 186 pages. This book is reprinted in 1981. And this reprint book can be seen below. This book is published in a reading book serie called "Delfinserien". This is book 681 in that serie.

Later they did publish one or two picture books around 1985. Based on the Max Trell stories?
Value around 5 Euro per book.

Bonniers 1981