I upgraded just one device to the new app. Most functions work for me with no issues. What I can not accomplish on the app, I do it on my Mac, which has the old app installed. My music library is functional, minus the few things that have been taken away, like the search function.
I like the new look, even though its a learning curve.
I have connected to two other systems at a friends house and at a recreation building. One of them is WIFI only and the other has wired components with a few speakers using Sonosnet.
I used the app for hours at both places without losing connectivity with either system
No. I do not regret upgrading. I am excited to see what the app will be capable of when all functionality has been restored.