This is just as it seems. They do not use water, chemicals, or electricity and don't require a functioning sewage system. In essence, by adding peat moss to the waste and treating it, the heat caused by the decomposing waste converts it into compost. It requires a vent to the outside in order to work so you'll need to do some remodeling to add this to your home or cabin. Installed professionally, a septic system is the best and most widely used of non-municipal sewage treatment.
Septic systems do require some water to flush toilets and to process waste.
If you're using gray water, it makes sense to use biodegradable soaps and detergents. If you have a septic system, have your tank pumped out in the near future and make sure it is working properly. This is really important. Waste must be buried deep enough to prevent animals from digging it up and also to prevent contamination of water supplies. Again, it is important to not just have a shovel, but to know where the water is.