No! It is not necessary to use rewriting tool. It is designed for the people with poor English to fulfill their needs. If you are a professional content writer, then it’s also useful for you. It will enable you to increase your vocabulary and synonyms memory. Recently, we have added up to 500,000 synonyms in this tool for english language and it will enable you to create content with more professionally.
So it is pretty hard actually to achieve unique and human readable article, but with little twists it can be done. I needed my wordai account just for FCS Networker, but I figured out that Spin Rewriter will fit perfectly for me because of their affordable price. If you need article spinner just for seo purposes, avoid them. If you want to create amazing articles, yes they are very good ..but pricey as ****…
I've ranked websites in the past with spun content, and now they are still on #1 position of google. First year (2014) google found me because my spun was really bad, many paragraphs were just copied and my position drop from #2 to around #20 after a panda update. Later I cleaned all my text with better spun (I didn't buy any article!), my ranking went up again, and with more backlinks I reached #1 and it is still there