[Nyororin]

Unfortunately, if your friend says it is a good way to "really" know the language... Then they don`t really know the language themselves.

It uses fake etymology to teach odd little stories so that you link the character to a specific single meaning... About half of which isn`t even the common meaning, and about 10% of being a meaning that only applies in some exotic circumstance.

In my linguistics course - in Japan, in a Japanese university - it was used as an example of how NOT to teach, and an example of the horrors of someone writing something for appeal and ignoring all levels of accuracy. The etymology professors were literally choking and gagging at it, and some of the stories given were down right awful and occasionally racist.