Simon 5 is coming soon!
Simon version 5 is currently in beta testing. It is a massive update, introducing a much-requested feature: syncing the Simon data between multiple Macs, plus a Simon Status service, a Link Checker filter, improved Find filter, iMessage and Speak Error notifiers, a new app icon, and much more.
Important: please note that Simon 5 requires a minimum of macOS 10.12 (Sierra), and will be a paid upgrade from Simon 4 after the beta. Purchasers since September 1, 2020 automatically get a version 5 license (that also works in previous versions).
Re: NEWBIE QUESTION: How best to use Simon to monitor...
Welcome!
If the sites show static content, you could just use the Web (HTTP) service and enable Smart Change Detection to notify you if anything changes on the page (and add desired notifiers).
If the content is dynamic (as is more likely), you can use Smart Change Detection to filter the HTML to just a critical area that shouldn't change, so you're notified if it does.
Another technique that could be useful is to specify just the Start text for something that is required, and leave the End text blank to include to the end of the source, or specify some End text. Then If either of those blocks is missing, it'll be a failure.
Hope this helps.