ANZ announced on Wednesday it was phasing out the Black Horse bank brand after the rights to the National Bank New Zealand licence ran out in 2014.
About $100 million would be spend on branch rebranding and repositioning of existing branches, with 20 branches marked for closure. That still left 280 branches, the largest network of New Zealand banks.
"The return on the $100 million investment appears limited, given the small number of branch and staff reductions.
While ANZ has implemented a number of initiatives to alleviate the revenue impact from the brand transition, we expect some revenue attrition, given the strength of the National Bank brand," Mr Timms said.
ANZ would spend about $340 million to integrate and improve efficiency in New Zealand, equating to 26% of the bank's cost base, including the money spent on the New Zealand technology integration in the past three half-year periods.
Given the large investment, a material improvement in the cost outcome in the business would be needed to justify the investments. That could be challenging, he said.
There were clearly some benefits on the cost side, even allowing for potential revenue attrition. However, whether those investments would be beneficial from the shareholders' perspective was under review, he said.
"We do not believe that ANZ will earn a sufficient return on the $100 million brand-merger investment without adding in other simplification benefits.
"The cost benefits are likely to be limited, as all frontline staff will be retained and the total branch network will only be reduced by 20."
From a cash earnings perspective, the impact would be favourable given the accounting treatment of the merger, he said.
