In Aybar, the Rockies add a left-handed pitcher who throws very hard. He is still somewhat raw, since he converted from outfielder to pitcher only a few short years ago. He will likely compete for a job out of the Colorado bullpen in spring training.

Since the Red Sox had already added Aybar to their 40-man roster, this trade helps them create a spot for some other prospect (or a free agent). In Koss, Boston adds an infield prospect with a good bat. He is still a few years away from competing for a job in MLB.

Aybar has some appeal in deep keeper leagues because he throws flames when he pitches. However, he should only be a late-round consideration for now. Keep an eye on how he progresses in spring training.