I use this system in my 5 full sized guitars now, and really like the peace of mind that comes with knowing it is properly humidified. That said, don't be surprised if the packs dry up quick the first set, as they are also bringing the case up to proper humidity if it was dry. I found that with my older Taylor in a case that hadn't been used in a while, then they lasted a long time after that.
For my Mini's I use the sound hole humidity system with an extra humidipak thrown in for good measure by the headstock. The one that is sitting out in the living room gets a drink every coupld of weeks.
Mr. Harry, maybe the packets that come with new products to keep them dry, if left in a closed container or ziplock bag would take some humidity out?