I've read up on it and found out that the system actually should prevent condensation forming inside the plane. The weight quoted is probably the average amount of condensation water in liquid form carried around in a plane.
I still don't understand how trapping it into silica gel will get rid of the weight though, unless the material is actually jettisoned in flight.
I also haven't found any hard data on how much power the units will require, power that will ultimately have to come from the fuel and will have to be offset against any actual fuel saving.