Eckart Jäde told me that user styles were not functioning on Garmin devices, because the .TYP-files should be in uppercase. The new versions fixes this.
Note that this site will hopefully have better availability than the previous download location which had been down for a few weeks.
Source code repository
The source code can be found at bitbucket, one can clone it using mercurial, the source is licensed under a BSD license.
Because I don't have a functioning GPS device anymore, I sadly can't test it myself anymore. :( Feedback is most welcome therefore! You can use the talkpage for this.