I know of Bigone exchange and I have used it once or twice and the experience was smooth, but about this USDT Fixed-Term deposit, am just hearing about it. From the name it looks like you will deposit some of your USDT which will be locked and maybe every Monday you get something out of it, this is just what I assume it is. However, before getting involved with anything about investing it's better to ask the team questions because they are the ones in a better position to answer correctly. Also, in situations like this, make sure you read the conditions surrounding it so as to be on the safer side.