http://wiki.i2p-projekt.i2p/wiki/index.php?title=DNS_registration
The bad edge is that a malicious person might host a registry, giving you wrong destinations, causing you to go to fraudulent eepsites, and potentially putting you in a bad situation (passwords being stolen, deanonymization attacks, etc). This is why there are only a few registry subscriptions in an out-of-the-box router, and why one should explore a registry before adding it to their subscription list.