I recently released a project of mine that does something similar but includes a variety of notification mechanisms, including web hooks. Also covers more than 120 different services.
I always struggle with what to include in a free tier. IE: How to balance the needs of supporting a service but also offering enough features for free to give them a taste.
I just launched a couple of weeks ago, after using it internally for months. Paid customers number in the dozens, which is enough to pay the hosting and other recurring fees.
My target is companies that are already spending hundreds or thousands of dollars a month on hosting services, so I would like to think that a few lattes-worth of peace-of-mind would be a worthwhile investment. Especially, given the time savings when you are hunting down a problem that's not actually yours.