By my count I think I have 7 devices which can be used as a cast point - 2 Google home mini (one is actually a Nest mini but they're the same device), a Google home hub, a Chromecast, a Chromecast audio and 2 Roku (one is a TV, the other an Express).
One of the neat things you can do with the audio only devices is set up groups so you can cast the same audio to multiple speakers.
In fact here's a screenshot of my Home app, on my tablet but this mirrors that on my phone.