Generally, I would be very careful who I give the custody of my BTC to. More precisely, I wouldn't give it to anyone. I especially don't like hearing numbers such as 700% returns on investment and similar 'promises' and 'guarantees'.
It is not exactly giving up custody, it is locking up your BTCB (a mirror of BTC on BSC) and getting ibBTCB (interest-bearing BTCB). I did some research as well and the crazy returns are coming from the leverage traders who use this capital and pay interest on it.
I have not looked at the contract you are referencing specifically, however, there are risks to lending out bitcoin (or any altcoin) on these platforms.
These types of platforms work like this:
The depositor send coin to the platform, which in turn lends out their coin to borrowers, who in turn put up collateral in the form of another type of coin. If the value of the collateral drops below a threshold, the collateral will be liquidated. The problem is that if there is a coin that is being used for a lot of collateral, if the price of this type of coin drops, the platform may not be able to liquidate the collateral at a rate that will make the depositors whole. It is difficult for smart contracts to manage this type of risk, as there being "too much" of a type of collateral being used is subjective and will require looking at outside sources.
If market forces are paying 7xx%+ APY of interest on deposits, the market is saying lending on this platform is high risk, especially if these high-interest rates are not "temporary spikes" caused by a sudden increase in demand for loans.
I will not endorse any particular lending platform. However, I would suggest that you review the rates being offered on centralized crypt lending platforms. One person in this thread mentioned celsius.network. There are other lending platforms out there that you can also review. These platforms should give you somewhat of an idea as to what the market is offering in terms of interest rates. If you are being presented with an opportunity that pays substantially higher than market rates, I would encourage you to consider why this might be, including if the market is believing that the particular platform is particularly risky.