@oscarf96, Welcome to the dark side!
It is possible that oomph is not letting DevStyle edit preferences (we have some compatibility issues with oomph). One thing you can try is:
1. Shut down Eclipse
2. Go to your .eclipse folder (usually at your home directory)
3. Remove every org.eclipse.oomph.* dir there
4. Launch eclipse and try again.
If that doesn’t work, could you also check if there’s anything interesting in the errors log?
Let us know any concern.
Cheers!