I've never looked into it but there have been a number of threads regarding it over in the Chess Books & Equipment forum. Here are a few links:
https://www.chess.com/forum/view/chess-equipment/the-woodpecker-method
https://www.chess.com/forum/view/general/woodpecker-method-by-axel-smith-and-hans-tikkanen
https://www.chess.com/forum/view/chess-equipment/woodpecker-method
https://www.chess.com/forum/view/chess-equipment/woodpecker-method-1
https://www.chess.com/forum/view/chess-equipment/chesscom-tactics-trainer---the-woodpecker-method
Has anyone here tried this one, descending into the circles of hell:
I’m gonna do it. Dante went to heaven through hell, so yeah, that must be the way to chess heaven.. and the gateway out of Purgatorio. I already love to look at lot’s of classical games, but that’s too easy and too enjoyable. I need some suffering, some penance, some blood, sweat, and tears.