Sicilian four knights: books vs chessable courses

[Chessbykermy]

Dear friends,

I’m considering to move to one of the sicilan variations: 4 knights variation to improve my repertoire with black, I’m a Breyer defence player.

So I have been considering to by a New in Chess book of 4 knights variation. The author is David Willis, USA correspondence chess player.

The second option I’m considering is the chessable course of Kamil Plichta as a possibility.

The problem I have in mind is the price, the book it’s about 30€ and the full chessable course is about 150€.

My question is: The difference of price is justified? Are chessable courses so good with that difference?
Do you have experience with chessable courses?

I would appreciate your opinions about this because I’m not sure about the best choice : buy the book? Or better buy the course?

Thanks!