Never let your audience guess what you are trying to say, your writing should literally speak for itself. When your content has too many errors, it becomes difficult to read and understand. Although, one or two errors can be skipped by readers, but glaring grammatical errors can minimize the impact of your content. Also, it can make your writing difficult to read and digest.
Google is getting VERY good at catching spun content so you'd better be talented at manual spins. If they DO catch you, of course they'll spank you... and hard. So anything you use spun content on is inherently AT RISK. Worse yet... Google gets better at finding spun/poor content every year. So in the longrun you're screwed. I'd weight your other options and see if you couldn't find a cheaper source for manually hand written content.
SpinnerChief works in a similar way by polling its huge Cloud Thesaurus for the statistically best synonym. As the Cloud Thesaurus grows, so it gets better and better at synonym replacement. The cloud thesaurus supports more than 20 languages, including German, French, Spanish, Italian, Swedish and Portuguese (both Brazil and Portugal), Dutch, Indonesian, Greek, etc...
Whe i first accessed the spin rewriter tool, i had one purpose on in mind, generate endless content to drive traffic, build authority and build backlinks. This is the way i found to move forward with any online business. I use the tool for 3 different purposes, money pages, 2nd tier backlinks and 3rd tier backlinks and the settings presented in the rewriter accomodate all three options flawlessly.

"One thing important in my business as seo provider is to generate unique content for my clients. I used to hire many writers to produce many articles manually costing me lots of time and money. Good thing that I learned about this great piece of software, now I can have many unique articles as I want with just a few clicks.The Spinnerchief team rocks! Highly recommended product"
While these recommendations give you some general guidelines as to what settings you want to use in these more popular situations, don’t be afraid to customize according to your needs. For instance, if your Tier 1 will build only just a few links, you can set the 1st input to “Very Readable” or even “Extremely Readable” as WordAI will still produce unique content even if only a few versions.