If it's a little tub you put silicone crystals in, and then they soak the water out the air and into a container at the bottom, then I have just bought one, and will be able to give you a better answer in a couple of days. I put it in yesterday, and it did seem to drop the humidity a little, only 3-4%, but I only half filled it with crystals, scared of overloading. I will put the others in tommorrow when the lights come back on. Someone else of here swore by it, so i thought it was worth the few £ it cost.
I found opening the a couple of windows and having a fan move air round the house helped too, but in general the air is moist at the moment so only made another small difference.
I'm just hoping constant air flow will stop any real problems...seems ok so far, so fingers crossed