Free downloads of thriller movies or books – which do you prefer?

Keyword analysis seems to be at the heart of becoming visible in the cybersphere. There are armies of online experts only too keen to give you free advice but even better advice if you upgrade to a paid service.
The issue I have with all these keyword gurus is that first, I can probably work out the best keywords for myself, and second, how do I know if by paying for an app or a subscription I'll be any better off? There are excellent keyword analysis tools such as google keyword tool and ubersuggest.org that do help to narrow down the choice of keywords by checking the number of times a word or phrase has been used. Often these program search by title + A or B, or C and so on.
Free movie downloads scores miles higher than free book downloads probably because more people watch movies than read books. Does this mean we have to include the more popular phrase in our SEO efforts even though the content may only bear a marginal relationship to the word string? We'll see if this blog attracts new readers because of my choice of headline.
I really became aware of this when I took seriously the keywords used to find ebooks on amazon and, more importantly, the book classifications. For those of you familiar with Kindle Direct Publishing (KDP) then you will know there is a dark art to the selection of which classification you book is listed under. It can make a remarkable difference, bearing in mind the number of titles in any particular group. 
Amazon allows you only two classifications from a drop-down menu but, don't be put off by this.
If you drill down into the underbelly of amazon you discover a hidden world of classification and sub-classification and then sub-sub-classification. You can ask amazon to reclassify your book (if you are an author/publisher) by providing a long string of classifications as you try to balance those with the least competition but yet with buying potential.
I've learned that I will have to change classifications on a regular basis to keep my titles popping up in searches by potential buyers who would otherwise never see any of them.
Self-published authors are used to grasping at straws in the battle for visibility.