ANZ's Sonia Ball said switching was popular with people who had made big purchases as it could be cheaper than hire purchase.
Claire Matthews, of the Massey University centre for banking studies, said balance transfers were a good way to hook customers. "If they didn't do well, the banks would stop doing them."
She said consumers needed to realise the interest rate would revert to the card's standard rate at some point.
And she said people who used a low-interest card to make more purchases could be caught out. The low-interest portion of the card would be paid off first, leaving the higher-interest new purchases earning interest. "You're only paying a low interest rate on the transferred balance. Any new payment is on a higher interest."
A person with $1,000 on a low rate who spent $200 on the card, then paid off $200, would find their low-interest amount reduced to $800 and their new purchase untouched. Matthews said: "It's important to understand how payments are attributed. They pay off the oldest first. If you are putting more purchases on, think about what you are paying compared to your old card."
Auckland woman Emma Consedine has a couple of credit cards with a total balance of $7,000. She could save $47 a fortnight by moving to one of the advertised rates but has not done so yet.
"I've thought about it but it just feels like a hassle. I think it would be worth it, for sure. I just haven't bothered."
Adviser Lisa Dudson said low-interest balance transfers could be a good tool if used properly. "The danger is that they move the problem sideways."
Some clients had transferred a balance and racked up more debt. "Moving from 20 per cent interest to 5 per cent makes sense providing you pay it off." There is no interest-free period on transferred balances.
Sorted's David Kneebone said people should talk to their banks before switching because they would sometimes match rates.
