Have done a couple of small systems with Yamaha MusicCast.
Just the WXA 50's so far.
Pretty easy to set up through the app.
GUI is different and some clients may prefer it to Sonos.
Once it is up and running, much like Sonos, I do not hear any complaints from the clients. It seems to just work.
Couple of advantages over Sonos that I can see.
Yamaha makes a number of things that have MusicCast built in, from speakers, amps, receivers to speaker bars. So I would think it should be easier to put together a house wide system that can integrate TV audio, surround sound and music together.
I also believe a few of the integration companies like RTI, Control 4 etc have drivers built to allow for control of MusicCast devices (have not tried them yet, so no comment on how well they work compared to drivers for Sonos)