It’s probably too early for you to expect any meaningful answers to that question. I suspect that very few of us upgraded to Sequoia, let alone tried out iPhone mirroring feature. I, for one, am waiting for 15.1 to upgrade my OS.
But I do think that this is a very handy feature. Not nearly as important as a standalone Passwords app, but handy.
I think this release is different to what has gone before. macOS 15 is not a huge change to MqcOS 14. It seems tighter and faster, possibly because the AppleAI should have been included, but it seems that it was not ready in time and has been put off until 15.1
I have upgraded both my MacBook Air M3 and MacBook Air M1 and the work really well. There are three small issues with apps, but they are minor.
It is macOS 15.1 that I will be avoiding, or at least putting off for a couple of months.