If you’re using a credit card overseas you’ll find the conversion occurs at your bank forex rate at the time of the transaction, plus typically in NZ a 2.25% – 2.5% conversion fee on top of this. Most travel cards have commission of around this when you load them, so you don’t actually benefit.
The big advantage of a travel card is being able to withdraw money from an ATM, however this is something I simply don’t do any longer. As I go to the US 2-3 times per year I always take a few hundred USD with me and find this normally lasts me for all my expenses for a couple of weeks as I just use my credit card for everything.
Most banks now charge around NZD$5 for a foreign ATM withdrawal so unless you’re planning on lots of withdrawals I find it just as easy to get money out from my own account if I need to.
Many people see the big advantage of travel cards being that you can lock in a currency, however unless you’re going to load significant amount of money when the currency is high (such as when the USD was at over 80c to the NZD) you’re only taking about very modest savings even if a currency drops by a few cents.
Each person is going to be different, so it really just depends where you’re going and what you plan to buy.