As far as your question is concerned whether SCANNERS ARE HELPFUL TO ACHIEVE GOOD MARKS in CA FINAL or not, then the answer cannot be given merely in Yes or No.
Scanners or Compilers are books where we find last years say 15-20 terms (8-10 years) question papers along with their probable answers
Q&A format books gives you the idea of the expected types of questions and the probable answers with reference to the sections/guidance available etc.
ICAI has changed its syllabus all through these years. So, you would also come through various topics which has no relevance in todays date.
If we leave the syllabus for one sec, we cannot ignore the changes/amendments/case-laws in direct and indirect taxes.
Based on my experience, i would suggest you to refer books available in Q and Ans formats from Paduka on FR/Auditing, Munish Bhandari for law/Dinesh Madan for ISCA etc for instance.
You can also opt for videos from various famous faculties for various topics or entire syllabus of your curriculum.
You can buy the books/videos from cakart also, use my reference code CAKARTAMB1671700 at the time of payment and get 6% discount . Share my code to your friends too.