Are spellbooks effective at all. They just feel slow and your near damned if the enemy swarms the field right off the bat. Then there's 30 vs. 20 cards. I'm guessing people who got kog with them were legend and people just didn't know how they interact.
Spellbook is definitely good, the grass version is unbelievably fast but it bricks a lot. The blizzard princess version is good and consistent even though it is slower than the grass version
Spellbook are easy to counter. They cant make a come back when you swarm the field with lots big monster. Additionally, it will be killed once the new box arrives
As someone who tested both 20 card and 30 card version, I could say both are KoG worthy. This deck is not simple though, and some misplays may not be very obvious, leading you to think that it's bad.
Spell books are one of the best decks out there and are a bit tough to play for ur first few duels but u get used to it and this deck lands u straight to legend and even kog with some more practice.
Although i find 30 version better for more summons and spellbooks.