Ah, this is great - I did not know it existed, just looked it up and saw it was released a few weeks ago with 2.5.0.153.
I was trying to solve the same problem, but for external alerts to these providers, Habitat’s native Email Notification driver is clearly the better default option.
The main differentiator for my Notification Gateway is that it is not really just an email sender. Because Hubitat calls a Google Apps Script endpoint, you control the backend logic. That means you can add custom routing, recipient groups, formatting, filtering, throttling or escalation logic if required.
So I would now position this as a lightweight HTTP notification broker rather than a replacement for Hubitat’s native email driver.
Hopefully it is useful for anyone who wants that kind of broker pattern.