Echoing others - not necessary but convenient. If you are trying to cut unnecessary costs, then don't get them. My family is not local, so our trips to
Disneyland are every few years and cost at least a few thousand after all is said and done. I spent $100 total for my wife and I,
(bought her one off Ebay that they no longer sell), and we'll have 6 days in the park. That's an extra $17 per day for an added convenience of just being able to tap and go and not fumble around with our phones.
This is especially important for us as our next trip is with our 1 year old and just being able to hold up our wrist for rides, entering/exiting the park, and photopass seems amazing. I know phones have become essential to the DL experience, but with MB you need to use them ust a bit less and I appreciate that.