As the author of this plugin I'm obviously biased.
I realise that giving the user the capability of defining their own CSS could be just as dangerous as giving them access to TinyMCE. But if it saves the author time then it can also save them money.
I used to frown upon the use of internal CSS, but now I'm a big fan. Using internal CSS can help reduce the size of the CSS file delivered to the browser. It's also less likely to adversely affect the formatting of other pages.
Note: internal CSS, also known as embedded CSS, is the stuff is put in the style tags. This is different from inline CSS - which is defined with the style tag.
I do have one niggle, which was that I had to fiddle with filters to handle strange behaviour with wpautop() processing. But I'm not the first person to have suffered this and won't be the last.
The problem is that there is a chance that activating this plugin will break the formatting of content that is relying on certain side effects of the default filters run for 'the_content'