You can customize the notification that really matters to you. It provides an edge to the existing phone/device notification system as it treats all notifications in the same way and with the same priority. You can simply choose a customized alarm sound based on the notification, like for alerts we have chosen some emergency threshold sound which gives us a reminder for purging activity. Good support on web and app for both Android and iOS. The charging model is straightforward based on one-time charges.

I love having access to Pushover's API, which makes adding push notifications to personal dev projects I'm working on. I also love the way you can use a variety of programming languages, including Python which is ideally suited for use on a Raspberry Pi. This makes sending push notifications really simple, and their API documentation is fantastically presented.