Though not a replacement for Mary's Horn, there are a few end-game situations in which you would want the range of a stringed instrument for Horde Lullaby and this would be a fine choice.
Kind of upset with all these people knocking this harp. This is a GREAT harp for Horde Lullaby. With a horn you only get like a 5m radius on horde lullaby. It won't tend to stick as well with a harp as it could with a horn, though, so I would recommend stacking on some Wind instrument skill and +CHR. Very useful for Dyamis, Einherjar, Puk ISNM, merit parties on Mamools, etc etc. Anywhere you need a good range on your Horde Lullaby ;)