Tether is a cryptocurrency provide users a stable alternative to other cryptocurrencies.
Because USDT/USD price keeps 1:1, USDT works similar to fiat currency in the cryptocurrency market, which have minor fluctuations.
USDT keeps a rate fixed to the USD, and claimed by its creators to be backed by one dollar for each token issued, though Tether Limited has not issued a promised audit of their currency reserves.
After Bitfinex, gate.io, MAX became the third exchange in the world to support both Omni Layer and ERC20 Token. Users are free to choose either version to fund in the MAX exchange and send it to other exchanges that support either version of USDT.
MAX will totalize the balance of both versions of USDT, and convert it to the version you want when you withdraw the USDT.
When you trade with USDT, there is no difference between two versions, they function the same, you only need to choose the version you want when doing fund/withdrawal.