Is my bank and financial data safe?

Yes. August tracks rent through open banking via Plaid, which is authorised and regulated by the Financial Conduct Authority, and the connection is read-only, so no one can move money. You can disconnect at any time, and your records remain yours to export.
A few notes on the choices. I left out "do I need landlord insurance", "is accidental landlord a legal status", and "can I sell the property later", because all three are already answered on the dictionary entry, and repeating them here would have the two pages competing for the same questions. The product page can simply link across to the dictionary entry for those, which is the reciprocal link we discussed.