0% slip if you just convert the HBD directly into Hive over 3.5 days.

Not really, there is still a chance you lose value even when you convert. You are not getting 1 USD worth of Hive at the moment of conversion, you are getting what witnesses consider 1 USD worth of Hive. (Also you have to sell that hive as well if you want to do something with that money, and voila what is that slippage you say.)

So realistically you get 12-13% which is okayish. I have a fund in Turkey that returns 18 to 19% currently. (Ofc, past performance is not an indicator yadda yadda)

It's so amazing people on the outside take one look at it and automatically assume it's a scam. That's how good it is.

Well, because they only see the APR that is written there and not what you actually get and I think they are right in a way.