What it teaches
Choosing between ó and u in words where the ear cannot help, because in modern Polish the two are pronounced the same.
The words are grouped around the rule that does most of the work: ó appears where the word is related to one with o or e in it — wóz beside wozy, niósł beside niesie. The exceptions have to be learned, and they come back through the review rather than being explained away.
What to look for
The endings are the reliable part: -ówka, -ówna, -ów take ó almost without exception. If those are solid, the rest is a shorter list than it looks.