Full-Text RSS is our product. It appears to be the component used in this WordPress plugin. Full-Text RSS isn’t really designed to provide optimal formatting. Its main focus is article extraction. You can remove HTML elements and attributes but then you’d have to create your own site configuration files for the site in question. I don’t know how much support there is for that in this plugin, so all I can do is point you to our own documentation on it.
Beyond that, you should do additional processing on the output in the consuming application. That’s what we do with PDF Newspaper and Push to Kindle (some of our other web apps).