It all depends on how many people are in your party. If it's two or less, you'll probably save money using the ZJZ. If three or more, free dining will be cheaper at a mod. (the dining will cost more to buy than the discount on the room for ZJZ is)
You can check online. On the disney homepage, scroll down to "great resort offers". That's on the bottom and than the right. Scroll down, and click "get started". Fill in your dates and partysize, pick the desired resort. At this moment, you'll get a quote for a room only code. Below the roomspecifics (like; standard, waterview, king bed etc.) you can add parktickets. Just pick what you want and click update. On the bottom of the same screen you can click "your package". There, choose the MYW incl dining and click "select". You'll now get a totall quote for your partysize and dates for the ZJZ-code. (it's a room-only discount -BUL/BUK code- with adding MYW tickets and dining). If you have difficulty online, or just like talking to a person more than the site; call CRO and ask about the ZJZ-code. It's a general public code. They can tell you within minutes how much your trip would cost with this code. If it is cheaper and you would want to change, they can do that also. (so you'll keep the same confirmation# etc.)