To quickly summarize what kind of risk we will be encountering using blockfi. #1 is blockfi will have the right to hold your withdrawal request up to 10 days according to the term of service TOS that you agreed to, so let say Bitcoin or Ethereum goes up (rally) and you would like to withdraw some or all of your coins from Blockfi to sell, but Blockfi decided to hold your coin for 10 days or so and by the time they released your coin, the rally might be over and you loss your chance of selling on the spike in price.
#2 risk is even though they say 6.2% APY but according to their term of service TOS that you agreed to, it is not guaranteed 6.2%, it’s up to 6.2%, so there will be chances that it will be lower than 6.2% APY, let’s hope it’s not 1% APY because that’s lower than your bank offering for interest account APY with cash, so probably not a good idea to buy Bitcoin and Ethereum with cash to invest in this Blockfi interest account thinking you will get 6.2% APY guaranteed. In addition to not getting 6.2% but you might end up loosing value of your original purchase of Bitcoin or Ethereum.
#3 risk is if the platform (Blockfi) get hacked and they loss your coins, they are not obligated to pay you back according to the term of service TOS. Although their wallets mentioned that backed by Gemini, what kind of relationship they have between each other is not 100% clear, is it Gemini wallet holding your coin through Blockfi, or Gemini insured Blockfi Bitcoin Ethereum holding? In any case, Bitcoin Ethereum are not insured at all neither with Gemini or Blockfi, so let say one day Blockfi or Gemini get hacked like mtGOX, you will surely cannot sue them easily to get all your fund back, but if they somehow have 10 Bitcoin left, then that 10 Bitcoin will get split between all accounts (thousands to hundred thousands accounts)
So those are the risks that you need to keep in mind when depositing your Bitcoin Ethereum to Blockfi interest account. The risk of the loan to someone and that someone don’t pay Blockfi back and you think that you will loose money, that’s not really the case here because there are collateral, more of the above 3 risks are greater.