The 1d6+1 damage seems a bit light, but it is going to be difficult to use as a melee weapon due to its design, hence the -10% penalty.
IMO I think I'ld rather up the damage to the 1d10 or 1d12 also increase the penalty to 15% or 20%, its two handed and a hit is going to be as good as one from a two handed axe even if the angle of the strike is skewed.