Two-weapon fighting with dire maces

[Zumbi]

Do users of dire maces benefit from this feat? Because altough it is only one weapon, it counts as 2 with dicewise

[Lucius]

Yes, all doubke weapons can use ambidexterity and two-weapon fighting to reduce penalties. It's almost the same as wielding two maces, you just get smaller penalties with the double weapon.

[Chongo]

Yes, a dire mace, unless for some reason changed here, will count as a medium sized weapon in the primary hand and a light weapon in the offhand.

You can liken this to a warhammer in the primary hand and a standard mace in the offhand.  That is, with all two weapon fighting feats (ambi, twf, and itwf), you will be looking at a  -2/-2 to AB on the primary and secondary hands.  This is opposed to the -4/-8 AB penalty you would face without ambi and twf.

Improved two weapon fighting (itwf) will also apply in giving you an extra offhand attack at the normal -5 penalty.