I think some of the reviewers of this product had unrealistic expectations. If you want to prevent condensation on your windows then you probably have humidity over 60% in your whole house and this little egg doesn't stand a chance. For that you would need to spend £100 mininum for a proper condensing electric dehumidifier and you'll be amazed how many litres of water that draws out of the air in your house. I actually have one of those too, which does a great job of keeping moisture in my house down to a comfortable level (which in turn reduces your heating bills as well as protects your house and contents from moisture damage).
This egg comes into its own if you have an isolated moisture problem in a confined space, like in a corner cupboard, where it just can't get sufficient airflow for moisture to be prevented. That's exactly the location I'm using mine and I'm sure it is helping. Roughly after 2 weeks I find the indicator changes colour meaning it has absorbed as much water as it can, so I put it in the microwave for 10 minutes and the cycle starts again. If that's the kind of moisture problem you're trying to avoid then I would recommend this product.