From their blog : " The reason we decided to add stablecoin markets was that the DGTX price fluctuations posed a problem for traders. For one, sudden drops in rate could turn a successful trade into a money loss, creating a negative user experience. We’ve also assumed that stability provided by USDC may attract traders with medium capital, increasing liquidity and traded volume."
Currently none exchange allows you to trade with no fees with taker order (market order). On FTX, if you stack FTT, you can have reduced fees but you still have fees. The same thing is planned with Digitex. If you stack DGTX, you could trade with NO fees. When you see how FTT token performed, I can't imagine about DGTX even is you can't really compare those exchanges. They deployed this update on their testnet some days ago.
Today you can't trade on low timeframe (<5min) on any exchanges because of expensive fees (Am i wrong ?). Digitex is trying to solve this problem and i'll not be surprised if this plateform got a lot of success in the next months/years.
https://blog.digitex.io/digitex-dev-update-7-trading-fees-and-usdc-futures/ 
