Momentum and Dual Striking can be used simultaneously. Dual Striking needs to be reactivated each time you enter a new zone, even if it seems active, to work properly.
Momentum does not increase movement speed.
There is a bug in core h.nss resulting in the loss of any attack speed bonus if the speed modifier is higher than 0.5. Activating Haste + Momentum corresponds to a speed modifier of 0.55, resulting in the loss of the speed bonus. Activating Haste + Momentum + Precise Striking results in a valid speed modifier of 0.45.