Why? Mandau has a better special WS, higher special WS multiplier (40% vs 25%) and higher DPS ( 31.02 vs 29.7) and it builds TP faster due to it's lower delay. Just don't put an Ipetam or Sandung in the offhand slot or it will drag you down. Leisilonu +2 is what you should be using offhand with a Mandau.