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.
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.