I'm particularly happy that iOS Chrome is now a "first class citizen". There were some shaky times before where it (provided you saved your form) showed the mobile view that Safari gets; then where it failed completely (with a JS alert()); where it showed the desktop modal (okay, but a bit janky) and finally where it had a made-for-mobile modal.

I'm a big fan of Checkout otherwise: it's definitely simplified things for me. I'd just like to see more communication regarding changes: I discovered most of those myself from my staging site.