Bluetooth has been cheap, easy, and popular for well over a decade. There are tons of bluetooth speakers and headphones for under $30 that can be set up in about a minute.
As far as I know (and I would love to find out that I'm wrong), there is no way to simultaneously broadcast music from one source to multiple bluetooth speakers.
When I have parties, I want to be able to play synchronised music in multiple rooms. I bought a bunch of used Google Home speakers for $40 each. They're great when they work, but they don't work very reliably.
I set up a group in the Google Home app, but some of them keep disappearing from the group, so I have to add them again.
Some apps don't natively work with Chromecast, so I have to either mirror my phone's audio or open the app in a desktop browser window and cast that. Both of those methods are pretty unreliable.
Google discontinued their Chromecast audio dongle, so you can't turn existing speakers into Chromecast speakers.
I'm willing to believe that Sonos or Apple works better, but the speakers are much more expensive.
JBL sells a bunch of bluetooth speakers for less than $60, but all of their wifi speakers are more than $160.
I realize that I've been ignoring the Amazon Echo Dot, because I don't want to give money to Jeff Bezos. I don't know whether or not I'm missing out on a good product. Is that the only option? Does nobody else sell a $40 wifi speaker?