FTR, iPhone XS Dual Sim is working flawlessly, and the UI is implemented well. It shows which sim on the incoming call screen, in the call history, and even on the Apple Watch, and it also allows you to choose which sim before dialing/SMS.
I put my US (Verizon) sim on the eSIM, and added a physical UK (Three Pay-as-you-Go) sim. Both work great, with zero issues. Less issues with the eSIM connectivity than I had with US physical sim back in November even.
Battery life may be impacted though.