My understanding is that the teachers that take on these roles are incredibly well trained, understand the responsibility, and know how to be both discreet and keep things privet. I believe a lot of the information available through this app was already being made available to the safeguarding leads in schools.
Challenging the use of this app is good, that's the role of these origination, checks and balances and all that. We need to be sure it is a net benefit for all involved. There is no denying though that if it helps teachers in safeguarding children that is a good thing.