Fandom Grammar

I would be more inclined to use dashes when there's a long phrase, rather than a few words, or if I'm trying to call attention to the appositive. If the sentences surrounding the queried example were talking about other wands of various lengths and makes, I might use em dashes to call attention to specifically which wand I meant. But if it was just being used to give additional detail, I'd use the commas to not call quite as much attention to it.

(And I am obviously quite partial to em dashes in general.)