The($179) is a very good portable WiFi/Bluetooth speaker that I last year. Now Sonos is releasing the , which is essentially the same speaker without the integrated microphone, for $20 less. It's available for preorder now and ships on March 15.
That microphone on the more expensive model allowed you to issue voice commands using Amazon Alexa or Google Assistant if the speaker is on your WiFi network at home, but could not be used for speakerphone calls.
Some people like having a voice-enabled "smart" speaker. However, for those who don't care about that feature, the SL gives you the option to save a little money. Sonos did the same thing with its Sonos One speaker, which also comes in afor $20 less than the .