Pratice Manuals are not at all sufficient, you need to refer module or classes or author books for it if you want to clear it in one go. You will clear with PM but for aggregrate you will need to refer module / classes / author books.
Law is one such paper where you can score good marks and can give you better aggregate as well. Your answering approach and the relevance of the content should be taken from practice manual. But don't stick to it.
As far as professional exams concerned, you should go through Munish Bhandari or Bare Act which-soever you find appropriate and try to solve questions stated in Practice Manual. If you want to grab good marks, Try to write Practice Manual Language.
Buy Handbook of Munish Bhandari. It contains all the Sections in table and charts forms. So it will easy to understand and remember. Handbook contains in summary form so you have ability to write a full answer form it.
Practice manual includes past examination papers so it reflects trend of examiners. Therefore practice manual is MUST but ONLY practice manual is NOT sufficient. It covers only some type of questoins but not the all. You must refer to referance books like Munish Bhandari.