I like how easy it is to integrate with Zapier, as well as having integrations w/ Slack / Salesforce etc! It's not cheap - but if you have enough projects or users of your product this could be worth considering (especially when compared against other providers). If we had more time before launch then maybe there would've been opportunities to improve some things in terms of UI UX design & functionality. We're using Zaps + API Gateway + Firebase FCM so far successfully solving our notification needs within apps such as Slack by triggering an action upon receiving push notifications via firestore events.