Claims to be GNU GPL, but only the Plug-in is. The actual editor is closed-source, but free.
Installation is not hard, but the product is split into two parts. You have to dig up the readme file to find out where to get the editor. Since a third of the reviewers did not even succeed in doing that, you can't say this is a good approach.
Now to the editor. Unfortunately, the problems dominate:
* Strips out valid header and paragraph tags from existing content.
* Doesn't have a clue about how to render multi-column layout.
* For whatever reason, doesn't access your template, so styles presented don't match styles in your style sheet.
* Insists on littering your HTML with an obnoxious 'Generated by' comment.
* Can't even specify common tags, like h1, p, etc.
One plus:
* The Screen Reader Preview is a nice option
Conclusion:
If this commercial company is hoping to generate sales for their 'Pro' product with this free offering, they will be disappointed. It is too few features, and screws with your markup too much, to compete with the better completely free offerings here.