In "Apply scaling themselves" mode, the X application will have to render itself at the appropriate size. This will avoid blurriness, but applications which aren't HiDPI-aware will render themselves at 1x scale and therefore will appear small.
In "Apply scaling themselves" mode, the X application will have to render itself at the appropriate size. This will avoid blurriness, but applications which aren't HiDPI-aware will render themselves at 1x scale and therefore will appear small.