Glad to be using the Sonos speakers as just AirPlay 2 speakers. No issues, no app to deal with (never even opened them past setup), perfectly synchronized with non-Sonos AirPlay speakers as well.
A lot of this could be solved if Apple put some basic engineering effort into the airplay UI, such as adding aliased groups. Every time I want to play to my effing speakers it's a 60 second ordeal.
Sometimes the little banner pops up from the top of the screen helpfully letting me to play to all of the speakers like I was before. Other times it not-so-helpfully suggests just playing to ONE speaker for some incomprehensible reason.
Still other times, the banner covers what I'm trying to see, and swiping it away seems to activate airplay even when I don't want to.