These balls are made of wool. The advertisement is specific in that it is New Zealand wool, but I doubt that is significant. The balls work in both electric and gas dryers.
For a gas dryer, the appliance directly burns a fossil fuel, which can impact the global warming situation. In both types of dryers electricity is used. The dryer tub must be rotated for either type of dryer. And, the heating element in an electric dryer uses electricity, a lot of electricity compared to a gas dryer. Of course not every location has gas service, so you may have to use what you can access.
Both gas and electricity cost money, and both can have a negative impact on the environment. With gas, as stated above, the burning of the gas is the problem. With electricity, the energy has to come from somewhere, and if it is commercial power that often has an environmental impact. Even if you have solar power, you probably use more than you make.
The balls are wool, so neither type of dryer will cause a problem interacting with them. If your dryer does not scorch your clothes, you should not worry about a heat source causing damage to the wool balls.
Find them at Sears.