I had one arrive yesterday and hooked it up today, was worried I'd foul things up somehow since I'd never replaced the Gateway before (my USG was 6 or 7 years old I think) but I just removed the old one, plugged in the new one, adopted it, and off we went. My cable modem seemed to need a reboot but that was it.

I had never enabled the traffic inspection stuff on the USG, so it was neat to finally get a look at that stuff after having it inactive for years. I'd been thinking about getting one of the UDM things but since the USG was working well I figured I'd wait until something like this came along. So far, so good!

This doesn't really seem comparable -- the big draw to the Express seems to be the WiFi built-in; at $149 for the Express vs $172 for the Gateway Lite + (at least) ~$100 for an AP, these are entirely different categories.

I hope they solved the cooling.