While I am well known here as a Glock proponent, I think this is a tough call.
The Glock is a tad lighter and slimmer. It also has a lower bore axis and much shorter trigger reset, which are advantages that become more and more important as you progress in skill. I wouldn't worry about the Glock being "pre-owned." I've never owned a new Glock.
But you already have an XD9. It makes sense to me to buy that gun's little brother for carry, rather than a gun with a different grip angle and different trigger. Practice with the big gun will translate more readily to skill with the little one.