This issue seems to happen on some Sierra or High Sierra systems. Your download size is correct so you don't need to download the zip file again. Fortunately you can bypass the blank installer problem by following these quick steps:
1) Find the installer file (VILabs Installer) and do not double click it; but right click on it and choose from the Menu - "Show Package Contents".
2) Open the Contents folder and open the MacOS folder.
3) Open this folder and you will again find the VILabs Installer.
4) Right click on this version of the VILabs Installer and choose from the drop down menu - "Open with" and then choose Terminal in the list of apps. The installation will then begin and you will be able now to set the directory for the installation process.
If this doesn't work, you can extract the RAR file manually as this is all our installer does. Unzip the downloaded file and open the data folder inside and extract the single rar file with the app UnRarX (free from here: http://www.vilabsaudio.com/download/UnRarX.zip). Then follow the rest of the installation guide from step 8.