Tbh we haven't tried internal speech on outsiders yet, just the two of us and one of our employees. We were able to solve it on that small set, so it's technically solvable with enough user specific internal speech personalization data. But the amount of time it took us to learn the behavior comfortably is a bit too high for us to focus on it as a key feature we have from the beginning. In a few months though we will start collecting larger scale data on internal speech as well.

Additionally, we found that you can mouth words discreetly enough / with no exaggerated movements, such that people sitting around you would likely not notice unless they were staring at you, which seems to be good enough, as a start at least.