You can treat the gateways as, gateways - simply for adding asset to your DEX account on BitShares. You don't have to trade any of their assets or other gateways. Then you trade the DEX bit-assets until you wish to cash out and use any of the possible gateways to do so.

Or you can use their trading assets that are backed and supported by the coins network wallet. This is more secure and traceable than any other Exchange you have to choose from, as they use of-blockchain books.

Without the gateways, adding other coins through deposits/withdrawals would be an issue.

PS. Fees are always visible

Either way, you choice every day.