I have an 06 and got the black one you show in the link for the AVO site. Dual console box w/ the curve (not flat at back on mine). This is different than an extended armrest, it adds the secondary storage box but is static vs. the one that elevates available domestically. The part # for yours is correct for the same product via Japanparts. No idea on Impreza parts.
If you want an actual "Extended armrest" based on the title of the thread this is probably what you want: http://www.subarugenuineparts.com/pr...roducts_id=593
which extends it and move based on setting.