I call BS on their statement that it's more cost efficient! Gas has more BTU than propane and you'll get more hours from 5 gallons of mixed/straight gas that you will with the same weight of propane.

"When you see that in order to produce, you need to obtain permission from men who produce nothing; when you see that money is flowing to those who deal not in goods, but in favors; you may know that your society is doomed." Ayn Rand