They are a team of 4. At that size, it's better for them to be focused on one thing than stretched out
On the one hand, a small team focused on voice-to-voice could probably do a lot better at voice-to-voice than a small team focused on voice-to-voice+text. But a small team focused on making the most useful model would probably do better at that goal by focusing on voice+text rather than voice-only.
At the end of the day, the released product needs to be good and needs to be done in a reasonable amount of time. I highly doubt they can do a generic model as well as a more specialised one.
But if you think you know better than them, you could try to contact them even though it looks they are crazy laser focused (their public email addresses are either for investors or employee candidates).