I think you are overreacting. Other, more popular messaging apps, also have prompts and yet they are used by hundreds of million of people.
In my opinion as power users we forget what regular users want and need, and are not willing to give up a little of what we like. But think of the benefits (phoneless sign ups and much much better private groups, to begin with) and tell me they don't outweigh the cons (a PIN prompt once every 2 weeks, in the marginal case).
In my opinion as power users we forget what regular users want and need, and are not willing to give up a little of what we like. But think of the benefits (phoneless sign ups and much much better private groups, to begin with) and tell me they don't outweigh the cons (a PIN prompt once every 2 weeks, in the marginal case).