That is one thing about the survival still that makes me not only keep one for myself.
I love that the survival still works no matter what is the heat source. If you can put a pot on it and boil water the still will purify it.
Today we use a homemade rocket stove powered with scraps of wood and twigs picket up from the ground.
The small twigs and inelegant build of the actual stove caused the still to work slower than normal. However, it was not a flaw of the stove, but more a flaw of the builder (me).
Actually the design came in quite useful as I got mud all over the inside of the still and since the survival still is designed to physically separate the dirty water from the pure steam my fumbling did not cause any problems.
I know that in the short term there are cheaper alternatives to this stove, but they all will wear out, be used up, or require replacement while the stainless steel survival stove will keep putting out pure water every day for at least one lifetime.