The export/import feature of J2XML via xml files works fine. It maintains article IDs so that article links still work, sometimes after some adjustment. Unfortunately this is not the case with weblink IDs so that article embedded weblinks don't work anymore. I had to do some changes in the database to adjust weblink IDs.
The 'send' feature could be a really nice one. It allows a direct transfer of articles from one website to another. But in my case it was only possible to send two articles in one step. So I couldn't use it for a larger number of articles.
Some room for improvement is also in the documentation. It is quiet thin and difficult to find. I needed some experiments to find out how J2XML works.
Nevertheles, the most important thing is that J2XML makes it possible to transfer Joomla articles from one website to another. Since it is a free extension, it may take some time to improve the other things.
Forgot to say, I released v1.6.3 of this module on the 14th April 2011 which along with other changes allows you to specify the width of the module.
Glad it helps!