If you were to use Tether then it's better to use your fiat. Tether has created by having the USD in mind. They say it's backed by USD 100% but it is not. It's just a smart contract and Tether company can close it anytime if they want.

It seems your basic about bitcoin is not clear. Bitcoin is a blockchain, a decentralized system which no one own it. Bitcoin is not here to give you profit and lose. It's a currency. But because of the demand in market the value against fiat moves up and down. I suggest you to read bitcoin white paper: https://bitcoin.org/bitcoin.pdf