It's no more or less safe. Provided you are using the exact same legitimate websites and they are using the same security techniques there should be no difference.
It is just as easy to be insecure on any device if you don't check you are visiting the correct legitimate website and that website is not using any form of security especially when filling out your payment details.
But provided you are sure you are on the legitimate website and all the necessary security is in place then it should not matter if you are on an iPad, Smartphone or a laptop.
Don't use public Wi-Fi networks for this, they use no encryption. The authors of the used apps would have to be completely stupid to rely on the connection encryption and not to use their own, but better be safe than sorry, you do not see inside every app.
IMHO The walled garden approach of apple apps being isolated from each other means an ipad is probably one of the safest methods and more secure than your computer or android.