Briefly they ran out of the translation card packs, but always had plenty of translators in stock. I saw maybe one kid with a translator in all the time I've been in the land... It's possible guests realized the card packs were as useful without the unit as with -or- they ran out due to a couple Ebay'ers buying all the stock in that first week. Either way, not their biggest seller by far, no.They were never "pushing" them, just showcasing merch to be sold on opening day.
And no idea how well they're doing, but I imagine not that good.