While compare with 3 screens is not yet ready for PDFs, it would be nice to use the suggested "curtain/fade/switch" style, which seens to be better than 2 windows screen. See video.
Want to have it in your own Meridian 2018 environment? Easy:
* Fin the file pdftronCompare.xsl under \inetpub folder in your server, backup it and replace with the attached one.
* Restart IIS
* Use Power WEB in Chrome/Firefox.