I am not able to see the video of these tutorials. If I could it is really a good job
My company reviewed eXist and it seemed like a good solution at first. We wanted an XML database with decent XPath/XQuery support. Once we started to use it with a bit heavier load, we found that the indexes got corrupted. (Same as Moritz's story). And once the data was corrupted, certain xpath queries would return no results even though the data was still in the DB. The worst part was that all of this occurred without any exceptions or errors being thrown. In our opinion, eXist needs to be more stable and reliable to be used in a commercial setting.