Would it be unwise to work with git master instead of a release? I need the features that have not been released yet like slotted pads but I wonder if my local library could get messed up since the file formats are changing still currently.
yes that would be unwise indeed, as stated in the readme. Also the application displays a very clear warning when you try to use it. So you need to wait for the next release (shouldn’t take too much time anymore to complete).
To be clear: You could use the git
master, create a project with that, export Gerbers, and order those. However, if you open the project with a later version of LibrePCB, there’s a considerably high probability that your project files will be broken and cannot be opened anymore.
If it’s a one-off project, that may be fine, but in general the
master branch is not meant for productive use.