The history of German-Polish relations is full of suffering and mutual recriminations.
Spiegel would say that.
If they can manage to do it, it'll be huge. It should be taught as common history, which it is - and the book should pull no punches.
The problem, of course, is that there is no common narrative. Germans would never admit that Frankfurt (Oder) was a nasty place to be a Pole in the early 1990's (many, many cases of Polish people being beaten up there) - nor would Poles admit that they actually enjoyed the "sealed" border with Germany.