The former kit is a useful accompaniment to your 6-pin Pmod (there are many, but an example of one is the PmodAD1). The extension cable lets you locate your Pmod six inches away from its host board, and the included 6-pin gender changer can provide extra connectivity to different kinds of boards.
The 12-pin kit is designed to work with your 12-pin Pmods (one of which is the PmodDA4). Like the 6-pin version, the cable allows you to extend your Pmod up to six inches away from the host board. Alternatively, you could use your 12-pin Pmod on a system board with only two 6-pin Pmod headers available. This kit also includes two 6-pin gender changers and one 12-pin gender changer.
Decide which works best for you (or both!) and check them out!