Firstly, I'm not sure what the magic is on this service within the USA now that T-Mobile and Sprint are merging. That was the original premise, that Fi would allow you to blend multiple phone networks for better service. It would be awesome if they managed to bring on another of the carriers and US mobile doesn't count for most of the US.
Having said that, the international roaming is the best offer that I know of from a US provider and I could easily see it being worth it for anyone who travels often. They also just added free calling to 50 countries on this unlimited plan, so that's also a great bonus if you work internationally often.
With the ease of adding a roaming eSIM, there is not much need to worry about origin of international roaming plans. You can get an eSIM2Fly (Thailand) or Three (Hong Kong) eSIM for roaming in all of Asia for under $5 per GB.
Having said that, the international roaming is the best offer that I know of from a US provider and I could easily see it being worth it for anyone who travels often. They also just added free calling to 50 countries on this unlimited plan, so that's also a great bonus if you work internationally often.