This is the only item for which you can redeem individual Coins of Ancestry, all the rest take five or more. This item is a good place to spend your excess Coins of Ancestry.
Like most event food, these dumplings scale with level, rather than restoring a fixed amount. The percentages restored per second are generous, restoring both health and mana. One dumpling will restore full health and 3/4 mana to any character, making this item a bargain for a high level character.
... on top of which, the mana restoration stacks with drinks.
... and, unlike many event items, these do not expire.
With 75 Coins of Ancestry you can by 600 Festival Dumplings - that's 30 stacks. Since they bind on pickup, you need to plan to have storage for them before you purchase them.