In an Auckland senior club match for Eden against University in 1924–25, Mills and Hector Gillespie shared an opening stand of 441.

He scored more than half of Auckland's total of 356, and more than Otago's two innings combined.

Dick Brittenden said: "Mills, lean and graceful, never seemed sufficiently robust for the demands of test cricket; he could probably claim to be the only test batsman who habitually wore wool, from neck to ankle, next to the skin.

A most graceful driver and cutter, he had the left-hander's penchant for the hook.

Spare and frail he was, but there was tremendous power which came from some hidden source; he was New Zealand's nearest approach to Woolley.