In summary, never pay a rental deposit directly to a landlord's personal bank account!
By law, a landlord must manage any rental deposit separately from their own assets (§ 551 Abs. 3 BGB). This is in order to protect the tenant and their rental deposit from any claims. For example, in the event that a landlord becomes insolvent.
So, why not use mietwise to make sure that you remain compliant and safe? 😉