I find that hard to believe. The "private investigators" that DKB alludes to are credit-scoring bureaus like Schufa, Infoscore or Experian. If you sign up for a German account that involves the extension of a line of credit, your bank will want to check your credit score, and for that you need to sign a waiver that they are allowed to exchange data about you with the above mentioned companies.

You would have to sign a similar clause with any German bank, whether it's Sal. Oppenheim, Commerzbank or your local Sparkasse or Volksbank.

But back to the topic - the DKB account comes with a few pitfalls, but if you use it correctly (i.e. only withdraw cash via the Visa-Card and making sure that your Girokonto, from which your Visa transactions are deducted, does not go negative) you can save a fortune on ATM fees. I've been a DKB customer for four years now, have used my DKB Visa for 150-200 ATM withdrawals (saving me over 600€ in fees over the years), and would not hesitate for a moment in recommending it to others.