I'd stick to using the BitShares DEX with the openSTEEM and openSBD. The volume has been low, but it poloniex having issues I hope trading will shift platform.
They are indeed both backed by another "central" exchange called OpenLedger, but there is no way to falsify or hide any asset holdings. It can't be taken down and you will never be able to lose your assets since the holding is decentralized in itself.