In main mode it is a twohander or a onehander when used with a shield (and uses appropriate 2h or 1h wpf), it gets a speed and damage penalty when used with a shield though.
In secondary mode (switch via x), it uses polearm wpf both when used with and without a shield (it can only stab with a shield then though).
There are also a couple of weapons in the 1h section with secondary mode, those are used as 1h with shield in main mode (at no penalty), and as 2h in secondary mode. Looks like you are better off trying one of those.