If it uses propylene glycol to regulate humidity, it will be partially two-way to a point.
PPG will vary the rate of or RH level depending upon its concentration. 50/50 mix with water will maintain a RH of about 70% as I recall.

As the ppg solution absorbs water vapor, it becomes more dilute. As it becomes more dilute, the humidity it maintains gradually increases.

Likewise, in dryer environments, the ppg solution releases water vapor, but also becomes more concentrated. The rh level maintained will gradually decrease in relation to how concentrated it becomes.

From Xikar’s site
XIKAR’s Propylene Glycol (PG Solution) maintains 70% RH. Distilled water evaporates quickly and creates humidification fluctuations. XIKAR's proprietary mix of PG Solution is calculated to match the water absorption rate with the rate at which PG biodegrades, resulting in a humidor that will not over saturate with PG. Maintains 70% RH for a "humidor fresh" smoke. Competitive mixtures of PG Solution often contain an incorrect mix resulting in a clogged humidifier
This statement that I emphasized “rate with the rate at which PG biodegrades” leaves some questions for me.