My experience with these products is that if properly used, they are quite safe. I've never had a leak or any negative experience in 5+ years.
The only drawback I've seen is in the summer when the humidity reaches 80% or more. The best the humidipacks do for me is to hold RH at the 55-65% level
and that's in a closed case. According to most authorities that is not a problem. The larger concern is in the winter, where I live, where the temperature drops and central heating blasts away drying the air to 30% or less. Then a humidifier comes to the rescue.