As the contact page and the FAQ require signing in, I can't comment on the exact implementation. I suspect they monitor Google's cache as that's the only publicly available data that can power this service. This is the wrong way to do it for many reasons:

1. There can be a delay between crawling and the page showing up in the cache. I've seen it to be on the order of several days in some cases, even though the page was ranking well and getting traffic!

2. Email is not a good log format. It's just not. I suspect for this service you'll need to enter each URL you want to monitor manually (yikes!) and then you get an email. If your sitemaps are any good, you already have a good list of your website's URLs and this could be a massive copy-paste operation, but then you'll get bombarded with emails. One time when I implemented such a system, GMail locked for days.

3. A much better solution is to do it server side with a proper log like in MySQL or MongoDB or whatever. You can do this with a cron job that analyzes the HTTP server's log files at the end of each day, does clever number crunching, generates a report and emails you.

Clever number crunching means calculating numbers that affect your business's bottom line. You can monitor percentage of pages indexed, segment by sections, do trends over time analyses, and more clever stuff like time between crawl and first Google-referred traffic.