The Or the Dryer?
The motor/fan assemblies in the two products are different with the Extreme model having more powerful 5.7 inch diameter motor/fan assemblies and the Airmax having less powerful 5.1 inch diameter motor/fan assemblies. It must be understood here that power is defined in this circumstance as motor generated torque. So, while each motor/fan assembly produces approximately 123 CFM free air (on the bench with no resistive elements at sea level) the 5.7 inch unit (Extreme) does so at a much lower speed (22,500 rpm) as compared to the Airmax at approximately 32,000 rpm. The amount of air pressure or vacuum (measured in water lift) that each unit produces in a free air condition and with the resistive elements introduced (dryer housing, filters, hoses, novels etc.) are also roughly equivalent. The primary distinction is that the larger motor fan assemblies (in the Extreme) achieve these objectives without having to work so hard which causes the motor to last longer. The current density at the brush to commutator contact point is substantially higher with the Airmax unit which causes the brushes and commutator to wear more rapidly which requires more frequent brush changes and a parallel reduction in general motor life.
There is a modest increase in practical air volume (measured at the nozzle) for the Extreme over the Airmax and a slight increase in temperature for the Airmax over the Extreme. This causes the units to have roughly equivalent drying capability with the Extreme having a marginal advantage in penetrating dense undercoats and the Airmax having a slight advantage in colder more humid conditions.
Accordingly, the primary distinction between the two products is generally motor related life expectancy. The Extreme does come with a 10 foot hose as opposed to a 6 foot hose and an extra nozzle as well. The Extreme also outweighs the Airmax dryer by several pounds.