I bought these for 2 quite specific purposes - for in a car, and in a wardrobe on an exterior wall, both to keep moisture down. I read the mixed reviews these dehumidifiers received, and decided to give them a try.
Since using them, the damp in my car is much reduced, to such a degree that I have just bought 2 more for other vehicles. The wardrobe was not too damp to start with, but I have confidence that these will keep it at bay reliably.
I have to say that people buying these should be realistic. They won't dry out a wet shower room, or solve a huge damp problem. They are designed to take some moisture out of the air, presumably in a closed area, and they do this well. If you have a bigger damp problem, buy an electric dehumidifier is my suggestion.
These are easy to 'recharge' by simply plugging into the mains. The observation window is very easy to read. I think that people should realise that this is just an observation window, not the full amount of crystals in there. The weight of these units is considerable, so I have to conclude that they are full of crystals, not just the small area behind the perspex as other reviewers have maybe assumed.
Overall, a good product if used in the environment it was designed for.