AD series is a DryCab with humidity indicator and humidizer unit only. There is only one control knob on AD series to set the power level to humidizer unit. The more power you set, the lower the humidity inside the drycab, vice versa. You will need some trial and error to set your desired humidity level on AD series.
DHC series, the Digi Cabi called it pro series. It is more expensive than AD series. It is have humiditity indicator with a feedback control to cut off the humidizer unit power when the humidity is lower than a preset level (and turn on again when the humidity is higher than a preset level), thus the humidity inside the drycab is more stable than AD series.