How is this different from donate to charity?
Donate portion shows up after the recipient has selected a non-charity payment method like PayPal or Virtual Visa. And only the recipients with enough reward value for their chosen payment method, and currency, will see the donate portion option. Lastly, you can decide from the full list of charities which you want to offer recipients and which you want to disable. So no need to worry about conflicting charities—only offer approved charities.
Will all recipients see the option?
Only recipients with a high enough reward amount and a low payment-method minimum can choose to donate a portion to charity. This means generally speaking, rewards for $20 and higher will see the option to donate to portion.