There are two angles for the stem, Comfort 10 degree and Sport 21 degree.

As you can read (sorry its in Dutch but I think its understandable), it seems that the one for Birdy II also fit for Birdy I (there are two other versions for the Birdy III).

The Sport 21 degree fits better for taller rider while the Comfort 10 degree fits better shorter riders.

Note that both adjustable stem have two positions with two different reach values (s (the reach adjustment is done by rotating the top part of the stem by 180 degrees and moving the push button to the opposite side of the stem tube, there are two holes in the stem for this push button)
Pacific Cycles has also a fixed one piece lower 19 degree stem (which because its fixed has also no reach adjustment possibilities, its always the shorter reach).