What was so special about the Apollo app?

I've seen the app Apollo as the center of the reddit protest (it was mentioned and cited more than any other app in relevant posts). I've also seen many Lemmy clients in development taking inspiration from it.

As a lifetime Android user I've never been able to use it, and I've never gotten a proper answer to "why not just use the official app?" What made it different from the official application and other unofficial clients that consequently made it so popular among Redditors?