Hi everyone, Alex from Aurora/IDEX here, just found this thread so wanted to address a few concerns.

1. The option for private keys is to allow people who so choose to have the best trading experience. Using a private key directly you don't have to sign each transaction so each order is instantaneous. The private key is stored locally encrypted in the browser and deleted every time you log out. For those who have concerns (totally understandable) we integrate with metamask and ledger.
2. Regarding the comment of getting paid to trade, that was the slogan we came up with for our market making rewards program (though I can see how in this space it seems extremely suspicious). Those who trade on IDEX will earn our network token, AURA, proportional to the amount of trading that they do. This token will enable people to run a node to support the future version of our platform and earn a portion of the trade fees for doing so.

Article on our rewards program - https://medium.com/aurora-dao/idex-aurora-decentralized-exchange-rewards-4e092c77affc
Article on our plans for staking - https://medium.com/aurora-dao/the-aura-token-share-in-the-success-of-idex-and-aurora-cf4212ba2e2a

Let us know if you have any other questions, we're experiencing great growth and just recently passed Etherdelta as the number one Ethereum token exchange and the most active smart contract on the Ethereum network!