Roflnadal

^ Sounds like big Schweser promoter.
If you comprehend any third-party or CFAI materials inside and out, you probably won't fail.
(I wouldn't say 'impossible'. Word is too strong for me)

I am also a big fan of CFAI materials. It maybe verbose sometimes but you get more in-dept understanding of materials.

Unless you have little time, I would use CFAI and use Schweser as supplement.