I have used this fan for quite a while. Never seemed to do much to help. It is noisy enough that you can't hear what people are saying to you if they are talk even kind of quietly.(Makes sneaking around with team mates hard because you can't communicate). A few weeks ago, my mask kept fogging up and the fan was doing no good so I took it off. My mask didn't fog up the rest of the day. I think it restricts more airflow than it supplies. All I know is that I havn't had much of a problem with fogging since I took it off. I was using it on a JT Proteus mask.
It is my personal opinion that this fan is a waiste of money. I am very dissapointed.