I think it is great when authors cooperate together as shown here. In series it can be hard for the orignating writer to keep going, and sometimes a another author can take a chapter and put new energy into the series, which not only makes it good for the original author, but also for the readers.
I have ask Guy to let me submit a chapter to one of his series and we have agreed. It is a lot of fun and of course the different twists because of changing around writers make for lots of fun.
CS