That’s what Extra Fuel claims to be. For emergencies.
And by “emergency” they mean “your failure to plan or pay any attention whatsoever to the fuel gauge.”
My Jeep requires 100% gasoline, so I have to actually plan out my fuel trips. That means I get nervous when I dip below 1/4 tank. I guess this stuff would be useful for things like boats and ATVs, but it seems to me the union of people who run out of gas regularly and people who buy this stuff is pretty small.