The aluminum-copper model also has visible ridges which reduce heat dissipation from the CPU. The noise emission exactly matches that of the copper-only model at 33.4 dB(A) for low speed and 44.8 dB(A) for high. The cooling capacity is, however, considerably lower: we measured 66 °C at top speed, and that's more than with the copper model at low speed. Not surprisingly, once you crank the fan down a bit the temperature rises to 74 °C and the processor starts to throttle. The copper-aluminum model is therefore not recommended for the newer Pentium 4 processors, but for older CPUs it's perfectly adequate.
The thermal resistance of this unit is 0.37 K/W. The cheaper NorthQ model can be had for around $37. However, bearing in mind the considerably better performance of the copper model that costs only a few dollars more, going with the all-copper unit is preferable.