Mitch Denny logged an issue against Controlled Vocab which I felt warranted a new release. It looks like those attempting to host configuration files on networks requiring authentication (e.g. SharePoint) may encounter issues. Mitch was kind (read brave) enough to navigate the code and submit a patch which made getting this out a lot easier. Thanks Mitch!
If this issue doesn’t affect you, then there is no need to upgrade from 1.5.1.