Pushover is fantastic, and if you are happy with it, then stick with it :-) I've never used Pushover, so I don't actually know all that well.
However, ntfy is 100% open source so you can self-host it if you like, and I believe it does have a bunch of features that Pushover does not (email notifications, email publishing, scheduled delivery, tags/emojis, phone calls, icons, ... see for yourself: https://docs.ntfy.sh/publish/). I'm sure ntfy is missing things too that Pushover has. I'll let you be the judge of it.
And yes, it's a reference to the song. Good catch. I was listening to it 20 years ago or something like that when I had to come up with a new username. And it stuck. ;-)
However, ntfy is 100% open source so you can self-host it if you like, and I believe it does have a bunch of features that Pushover does not (email notifications, email publishing, scheduled delivery, tags/emojis, phone calls, icons, ... see for yourself: https://docs.ntfy.sh/publish/). I'm sure ntfy is missing things too that Pushover has. I'll let you be the judge of it.