This is definitely one of the better options among the spinners that we have available right now, with great customer support – which I had a pleasure of dealing with, they were helpful and fast to respond. Actually the whole team behind this product is very professional, I know a couple of them and dealt with them in the past, they an alright bunch.
Nobody is immune to spelling and grammatical errors, not even me. It doesn't matter how many times you proofread your content, sometimes an error slips through the cracks. But, too many errors in your writing are bad for article writing services business and can also hurt your reputation over time. If customers are annoyed by poor grammar on social media or on a small blog post, just think about how they will feel if they receive an email or eBook laced with these errors.
Imo it is not possible for google to detect properly spun content, it is not worth computing power it requires. They can do this using ngrams for example, but it is uses a lot of queries. And for example article spinner I coded beats this algo, so google cant detect that the content is spun. Manual spinning is also good but it takes more than 30 minutes per article.