OlivierV I'm not sure how it works and who has access to what.
The accounts are completely isolated. The only thing that happens is that the initiator pays the bill of €19,99 and has to request the money from the other participants. So, theoretically, someone could not pay their share of the bill, but then you kick them out and find someone else. Most initiators require upfront payment, in case someone doesn't pay then you can still quickly find someone else for the remainder of the month. Only the Pack owner can see the name + public avatar of the persons in his/her Pack. Nothing else, nothing about usage, IBANs, messages, nothing.
The other way around, as a participant in someone else's Pack, I cannot even see who else is in the Pack. The only thing I see is that my membership is "bunq Pack", and I can choose to leave it. As participant I cannot even see the name/picture of the initiator of "my" Pack (or not that I know of at least). You theoretically risk being kicked out of the Pack after being paid; your theoretical loss would be max. €5,-. That's a small risk you need to consider whether you are willing to take it or not. Even when you get kicked out it is not the case that everything stops working: you will be reverted to Premium, and all your IBANs etc will remain as usual. 🙂
Hope this clarifies the matter, there is little risk to sharing the Pack with strangers, but I completely understand that not everyone is up to it. 🙂