Interesting... so I think the difference for Hydranet (HDN) is this:

Hydranet works by:

1) Allowing users to move their assets from any supported chain (BTC and EVM chains [ETH, ARB, BSC, etc]) to the L2 equivalent for that chain (Lightning for BTC, and state channels for EVM).

2) Through an order book, HDN connects users directly to facilitate swapping of assets over L2, including cross-chain (IE, BTC on Lightning for say ETH in a state channel)
  2a) So if I had BTC and wanted ETH, I move my BTC to lightning, and then I am able to trustlessly swap my BTC on lightning for someone else's ETH in a state channel. This swap is a virtually free L2 transaction (compared to on-chain fees for BTC or ETH which can be substantial) and I only have to pay a small DEX fee. It is also being completed in SECONDS versus minutes for say Thorchain on-chain swaps

3) At all times I maintain custody of my assets. There are no wrapped assets involved, and I can move my L2 assets back to L1 whenever I want.

4) Bonus: I can also swap say USDT on ETH for USDT on ARB, provided I start by moving my ETH USDT to a L2 state channel, then swap as above. Completed in SECONDS for low cost, certainly orders of magnitude less than current bridging solutions.

Is my understanding correct? If so, this DEX is very different than any other solution out there. It's a CEX like experience with the order books, but is a DEX where you never have to give up control, no wrapped assets, and can act as a cheap bridging solution, and completes swaps quickly in seconds. Almost too good to be true, and if all the above is correct, seems like a game changer to me.