Why do I need an account to share?
When you share, your list and every change need to travel from your device to the other participants' devices. Since everyone is rarely online at the same time, this data is briefly cached on our servers (located in Germany) for that purpose — solely to pass it on to the authorized participants.
The transfer is encrypted, we analyze nothing in the process, and we deliberately ask only for the essentials: name and email. That's exactly what an account is for — it assigns the right changes to the right people.
Your trust is protected: if you delete your account, this data is removed from our servers immediately. And everything pon learns (order, locations, pantry) stays local on your device anyway and is never transferred along. Without sharing you don't need an account — then nothing leaves your iPhone at all. An account is also worthwhile if you want to use pon on several of your own devices (e.g. iPhone and iPad) with the same state.