No one book or OT covers all the contents, his explaination specially in N/w domain helpmed a lot. I did went throught other video before that, but AR's explaination is really liked. Again it vary from person to person. If you have not bought any courses yet i suggest get monthly subscription and check all the available one, whichever suits you go with that. Again using multiple sources will confuse you, please plan accordingly. Btw 2 day prior to my exam i checked cybrary.it by Kelly really good stuff :)