When you integrate Perfect Tense with WordAi, Perfect Tense will check any text you spin for grammatical errors. Perfect Tense will then add those spelling and grammatical errors as synonyms. This means that your spintax will be more unique and more readable. When using Perfect Tense with WordAi, your spun content will often end up even higher quality than the original.
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