The tax advantage for currency ETNs is history.  With currency ETNs, one could buy the FXE for example which directly represents British pounds held and interest paid at the prevailing rates.  These ETNs would not pay the interest directly to the shareholder, rather, they'd apply the interest to the value of the ETN itself.  Therefore you would not have to pay tax on this income until you sold.  Second, since this is/was considered a "pre-paid contract", the taxable rate was 15%.  No longer.  The tax rate can now be up to 35%.