I'm not sure, never looked into them properly. Maybe Hive account@good-karma can give us some insight on that.

I'm assuming there's limits and it's not offering just self-votes back but also something that highlights your posts on their dapp as it goes through it. I also doubt the focus there is to maximize rewards for posts and returns for delegators where that's the main shtick here with hive.curation.

As you said yourself the 16% APR is too good to ignore, yet you ignore the effects it may have on the ecosystem or your investment in general compared to proper curation and distribution of inflation.