I've had Sonos for over a decade. Started with a Play:5. Decent enough. Definitely not audiophile and doesn't compare to my B&W CDM 9NT speakers, nor do I expect it to, but I did hook a Sonos Connect up to that system for the better audio quality of those speakers. I also eventually got some Play:1's, a Playbase, a Sub, and a Sonos One.
Sonos eventually rendered my old system incompatible with itself. The older Play:5 and Connect are not compatible with the other newer speakers. If I try to play through all of them on the legacy app, the sound keeps dropping out. Their solution is to buy more of their stuff and junk my old perfectly working $500 Play:5 and both of my $350 Connects. Yes. That is over $1,000 in equipment they want me to junk.
Well, with the Echo, you can take the 1/8" jack and output audio to any type of amp and speaker. If the tech in the Echo becomes outdated, just get a new cheap Echo instead of throwing out $1,200 in equipment. In fact, I had an old, but good quality 100W/channel studio power amp in a rack and some decent bookshelf speakers, just hooked an Echo up to them, and they sounds way better than the pair of Play:1's that were originally in the room... And it still would have been cheaper if I bought everything new instead of using stuff I had lying around.
Granted, the audio quality of the Echo output isn't audiophile quality. However, if you pair it with a better speaker, it will sound better in many respects than any of the Sonos speakers. Also, if you want better quality audio, just get the Echo Link. Best of all, you won't be forced to throw out a perfectly good amp and speaker when Sonos decides to render the streaming portion obsolete.