I am working in online content writing services company since a couple of years and i have total five year of content writing experience. And I think small SEO tool is a most helpful tool for a content writer. For plagiarism checker, Turn tin is the best tool but Turn tin is paid tool and small SEO tool is a free tool and shows correct plagiarism.
I think R&D helps more in content writing than using tools. You must refer blogs in your niche to get ideas about your content and keep on researching upon the writing style which is considered as ideal to serve more useful content to users and keep them engaged.