It bears mentioning (if I haven't already) that the readability of any spun article you create using Spinbot will depend greatly on the quality of the source article that you want to spin. Spinbot will not, for the most part, correct grammatical errors, as this would only duplicate the functionality of countless, already existing word processors that will accomplish this job for you (Microsoft Word, for example). Rather than duplicate existing word processor functionality, Spinbot is designed to fill a gap that currently exists in the article creation world, which is to rewrite readable text into more readable text.
Thus, to get maximum bang for your "click" you should make sure that any article you want to spin has been checked for grammar and spelling mistakes. On a related note, if you are attempting to use a figure of speech that doesn't sounds quite right to begin with, Spinbot will probably make it sound even more off base since the underlying logic assumes that you wrote the article correctly.
Spinbot assumes that any article you enter to be spun is already correct, grammatically, syntactically and idiomatically.
That being said, go out there and spin some articles!