I activated an 3HK esim in US on AT&T with iPhone XS. It took ~ 30 min and I manually connected to AT&T (3HK US roaming partner) while waiting for activation confirmation sms. A few others on flyertalk and reddit have reported activating outside HK if you dig around, though I wouldn't be surprised if YMMV based on roaming network. The 3HK management app is not available in the US app store. I had no issues purchasing an additional 1 day package with Chase Visa and haven't used it, yet, so can't confirm performance or how to keep it valid.

Also FYI, activating any eSIM + Verizon physical sim results in the Verizon app not being able to load Verizon account details & timing out. The Verizon website still works as it prompts for account login. This was also reported on reddit a bit after the dual sim iPhone was released and I recently reported it as a bug, too.

esimdb blog details some of their experiences with using and reloading in Japanese
https://esimdb.com/ja/blog/tag/3-hong-kong/