On the actual site for these digital addresses [1], they mention some risks and countermeasures - translated:
> Risks and Countermeasures When Using the Service
> 1. Obtaining a Digital Address involves the following risks. Please use the service after understanding them.
> a. If a third party learns your Digital Address, they may be able to determine the corresponding address.
> b. Randomly entering a Digital Address may display the corresponding address.
> 2. Our company anticipates the above risks and has prepared the following mechanisms as countermeasures.
> a. Digital addresses can be deleted immediately, and the linkage between addresses and digital addresses can be disabled. Note that even if deleted once, a new digital address can be reacquired.
> b. The system has mechanisms to detect and prevent abnormal searches, such as a large number of searches in a short period of time.
> c. Even in the unlikely event of a personal information leak, our system is designed with leakage risks in mind to prevent personal identification. Digital address data is managed in a separate database from personal information such as email addresses and phone numbers, as shown below.
1a. is the primary concern for me, and while I can disassociate my identity from a digital address, that would defeat the purpose of using digital addresses to e.g. handle the case when moving. Sounds like they don't have a real answer to this security issue besides just accepting it.