Okay, since my copy arrived about 30 minutes after my above post ...
The widget in question is
DashBlog. And, unfortunately, it doesn't work.
First of all, it's a generic widget that uses the Blogger API to make the posts. Not a problem, I thought, that's what my blog plugin is for. But while the widget can successfully log in and get a list of the available blogs/sections to post to, posting itself does not work.
A quick debugging session revealed why that is so: It's using the Blogger 2 API, but the blog plugin only understands the Blogger API version 1.
So either someone has to tell the widget's author to support the older API or someone has to create another widget.
I have no plans to implement the Blogger 2 API as it has been discontinued (never been officially released, actually) and has since been replaced by Atom.
bye, Dirk