HY (unified asset) is in essence a multiledger step towards the final hybrix protocol. At time of writing TOMO.HY and ETH.HY are joined together, and can effectively be seen as one asset. We are now working on a bridge between the two to make interaction between both ledgers seamless. If you would like to make a HY transaction, the wallet.hybrix.io wallet will automatically choose the cheapest chain available in terms of transaction costs. Currently that will be TOMO.HY where the fee is very low, and denominated in HY (the fee is given to miners in the Tomo network).