This is absolutely useless. It claims it rewrites English sentences, but it just offers words alternatives, which is only nouns. Also, most of those suggested alternatives are unable to use. If you see their maker's home page, Whitehat Box, you can see numerous people request the refund. It's far from western progressive software like Grammarly or sketch engine. They stole my money with the diceiptive advertisement.

Unlike other spinners, WordAi fully understands what each word content means. It doesn’t view sentences as just a list of words, it views them as real things that interact with each other. This human like understanding allows WordAI to automatically rewrite entire sentences from scratch. This high level of rewriting ensures that Google and Copyscape can’t detect your content while still remaining human readable!
This excellent article rewriter tool will thoroughly scan your entire content, looking for the words that it can replace with a synonym. All the words that it replaces with a substitute will be highlighted in the bold and colorful text. By clicking on any of the highlighted words or phrases, you can see the original word, suggestions or add your own word. Also, you can click on the original word to revert or click on any other word to replace.
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.
Coming up with content can be tough for those who are new to niche blogging. So it’s not surprising that some people turn to article spinning software, in hope for a better solution. I’ve always been an advocate for creating original things, but in this WordAi review, I got curious and decided to do an experiment to see how a spun content would look like. Are there any benefits to use this type of services at all? 
Cross Platform – Being a Mac user I prefer when I can fire up a program locally. WordAi is web based and therefore works on Windows & Macs without issue (Linux as well). SpinnerChief III Ultimate has a Web Api that allows spinning from the web, but we did not have much luck with it, so at this time we consider SpinnerChief a Windows only application and therefore requires me to run it in a virtual Windows Machine using VMWare Fusion. This one is a hard one to call because clearly WordAi wins cross platform, but it doesn’t have all the extras that SpinnerChief offers.
A website with lots of unique and human-readable content is going to give you the best ROI. The more quality readable content your website has, the more exposure it will get from major search engines such as Google & Yahoo. But creating unique content takes time as you first need to develop content creation strategies and then you need some hours to write a full SEO optimized content. How great it would be if you can produce quality content within minutes! Yes, it's possible with the help of this free Article Rewriter Tool developed by SeoToolStation. 

Some article spinners out there require you to enter your text with properly formatted spintax to create the end result. To create formatted spintax, you'll usually need another tool. But Article Rewriter by Small SEO Tools doesn't require that. Instead, it does all the thinking for you, from taking in the context of every phrase to creating additional textual content that is as readable and meaningful as the text you originally entered.
From personal experience Spin Rewriter is the best! like I still use it today. Its so easy to use (Just copy paste and the program do everything) Because of this tool I managed to schedule content and articles for 3 years, do you know how much time and money I’ve saved?!?! A LOT!!! Also i high recommend you pick their mothly plan if you are still in doubt