The only downside is that you have to be willing to wait and keep your balance blocked for 365 days for a 60% APY (fixed-term).
I have checked and found out that in order to get 60% APY (boosted fixed term), you need to fulfill some wagering requirements as well, while in fixed term (27% APY), there is no requirement of any wagering.
How much wagering.
Apart from what @AHOYBRAUSE has suggested (which is a quite good explanation), I am quoting the relevant section from the official document of the casino in question,
you locked 1,000 USDT in a 30 days Fixed-Term with Wager Pool. The multiplier for this pool is set at 3 meaning that in order to receive the APR displayed for this pool on the Staking Page, your last 30 days wager at the moment of rewards distribution has to be at least 3,000 USDT. In the event that at the moment of reward distribution your last 30 days wager is below 3,000 USDT the platform will distribute the rewards based on the APR of 0%.
Minimum wager requirements for each lock period are expressly stipulated on the staking popup. Minimum wager requirements can be modified at BetFury’s sole discretion. In case of any modifications to minimum wager requirements, the updated amounts will be depicted on the staking page but there will be no announcement via social media channels.
I strongly advise everyone to go through the terms and conditions in detail before thinking of staking. It is very difficult to handle the downswing in wagering, especially if you are not experienced. You can easily lose all of your money chasing the wagering requirements. It is not just the question of wagering as per house edge and accepting loss but you need to be psychologically trained not to chase losses.