So to get cashback you have to buy and hold Binance's token, and your cashback is paid in more of Binance's token? Seems like a pretty good way of artificially pumping the price of their token more than anything else. They don't actually have to pay out anything in cashback here, because if a users wants to convert their cashback to BTC or fiat it will be other users they are selling their BNB to, not Binance.
Also, make note of the following:
Binance utilizes a third-party KYC provider and there are some instances where the state data does not get properly recorded.
As with everything to do with Binance, expect your personal information to be splashed around an unknown number of servers controlled by a bunch of unknown third parties and potentially hacked or leaked in the future.