Worth it compared to what? For $14.99 you are basically buying the 22oz
DCL glass beer mug, which is actually a pretty nice mug, and the ability to have it filled at the 16oz beer prices for the duration of your cruise. If you weren't planning on bringing your own beer on board, it therefore represents about a 20% savings on the ship prices, which is still pretty steep, as I'm sure you know.
Draft beer selections will vary somewhat from one bar to another on the same ship, and will vary slightly over time as some beers fall in and out of favor with DCL. In addition, you will not see a very extensive selection, perhaps 3 or 4 draft beers available at any particular bar. For instance by the pools you will tend to see lighter lagers: Budweiser, Bud Light, Shock Top, Michelob Ultra, Michelob Amber Boch, Heinekin. In the nightclubs you will see a more higher quality selection of lagers and ales: Stella, SamAdams Boston Lager, Sierra Nevada Pale Ale, maybe a SamAdams Seasonal, Guiness. I am not saying all these will be available on your cruise, only that they represent the kinds of beers that might be available based on what we've seen before. If you're a really picky beer snob, you're probably going to be a little disappointed with the selection. Personally I'd love to see some better quality choices, but you have to remember DCL is trying to please the 'average' customer and doesn't have a lot of extra space to provide for dozens of alternatives.
The 'token' is essentially a small paper card that takes the place of the mug, if you don't want to carry it around with you. So you have a beer in your DCL mug, when you're finished you can bring the empty mug back to any bar and swap it for a beer card, which you can then turn back in for a new clean mug at any bar next time you want to have another beer. When you leave to go home, you can either pack a clean mug to bring home as a souvenir, or keep the card to bring back with you next time and do it all over again. As stated before, the mug is actually pretty nice, very heavy glass, not a cheap crappy souvenir at all, so I think most people bring them home. At least that's what we do.
Hoping that helps. Have a great time!