This is a general problem with Windows 8 and not specific to DisplayLink displays. There are a number of articles on the internet which describe the issue and offer workaround for the issue. For example:
How to Make the Windows Desktop Work Well on High-DPI Displays and Fix Blurry Fonts
How do I fix desktop app display issues?
This behaviour has been improved on Windows 10 and there is a good description on scaling and the problems it addresses here: