In their FAQs for their app, they state, "We are launching data-only plans with our first update, so you won't need a new number. Stay tuned for our voice plans launching soon, together with additional local numbers."
That's the part that seems promising. In my last trip to Vietnam, I found the (essential!) Grab app, the local Uber-alike ride-hailing service, now requires a local number. It didn't six months ago. This seems to regard drivers wanting to be able to call their riders if necessary. However, the language barrier would seem to render that nonsensical, and countries such as China do just fine with their apps (such as China's DiDi) providing serviceable translation of text messages in both directions.
Anyway, that's one use-case that requires a local number.
The TruPhone app has been updated and now loads on my phone without crashing. Won't be using it until those voice-number options are available, though.