The benefit of the mug is a larger serving of draft beer (approximately 21 oz.) for the same price as a 16 oz. serving, about one-third more. This works if one is happy with the draft beer options. These vary among the different bars, lounges, and dining rooms where adult beverages might be purchased. If there’s a preference for bottled or canned beer instead, the mug provides no particular benefit. This might be the primary consideration for your man.
Once purchased, the empty mug can be exchanged for a “beer mug token” to avoid having to carry around the mug between uses on board. At the end of the cruise, simply keep the last mug as a souvenir of the cruise or do one last exchange to get a token for use on a future cruise. I have two mugs at home (one I purchased, one gifted to me by DD from one of her cruises) along with a beer mug token that I’ve exchanged many times during more recent cruises. I’ll have my token along on our b2b cruises on the Magic starting this Sunday. I’m fine with exploring the draft beer options, although these could be better, as I generally prefer draft over bottled beers and almost never drink canned beers except on picnics or at barbecues.