The CFA syllabus is huge and the CFA Institute books do full justice to the subjects, both in depth and width. For best results in your exam, you are recommended to study the Institute books and practice all the problems and exercises in them.
However, practically it may become extremely difficult to go through each of the 6 odd books of roughly 1000 pages each if you are also simultaneously working or studying elsewhere. Some of the books do get a bit verbose and it can be challenging to cull out the important elements from the not-so-important ones. This is where a guide book like Schweser can help you.
So while we strongly recommend that you DO NOT depend just on guide books, we think the Schweser books are an excellent supplement to your Institute books.
Scores of candidates have used Schweser materials along with the Institute books as a guide.
Schweser books should be used as a supplement and not as a replacement for or a shortcut to the CFA Institute books. If you are really short of time, you could use Schweser books alone for 1 or 2 Study Sessions at the most.
NOTE: The topics in Level 1 that you should definitely NOT depend just on guide books are:
• Ethical and Professional Standards
• Financial Reporting and Analysis
The above 2 topics together alone constitute ~35% of the exam content and cannot be taken lightly. Ethics especially is not very well covered in any coaching book and is best studied from the CFA Institute book.