So my XS max is the first iPhone I've ever owned (used nexus/pixel phones for a number of years, and other android before that)... but I think the double click to use apple pay is perfect. Maybe it's because I hadn't become accustomed to a different way of doing it on older phones, but it's great IMO.
Aside from that, usability with no home button is nearly identical to my Pixel 3 with the latest version of android. Everything looks and feels nearly exactly the same. The only thing I miss is gesture control for going back. It works as a part of instagram on iOS, but I had that same functionality across any app on my pixel and it was great.