Safari extension for web page change monitoring

Any good suggestions for a Safari extension to monitor web pages for changes? I know there’s 3rd party services for this, but I hesitate to give my email to a “free service”.

What a coincidence - your screen name is Simon, and Simon might be the answer to your search. Not a Safari extension, and not free, but……

There is also this: ‎Distill Web Monitor on the App Store