Never used the Elos products.
Fuel is mostly a blend of amino acids (a nitrogen source, btw) and organic carbon. There are trace elements and vitamins too.
SeaChem (IMO) has attempted to make an 'all in one' carbon dosing product which addresses the low nitrogen paradox that inevitably occurs in 'ultra low nutrient' systems. By many accounts they have succeeded (if people would follow the directions explicitly). Done correctly you will control both nitrate and phosphate in your system.
The problem as I see it is many people don't know where to stop. Some nutrients are required for life.
So,
They either over do it and crash their tank, or drive the levels so low that their corals begin to starve and lose their color. Both are wrong and bad things to happen in a reef system.
Carbon dosing requires some understanding of what's going on (how it's supposed to work) a lot of patience and the discipline to test regularly until the dosages and nutrient levels are all worked out.
One day I envision a 'recipe' that will allow for an easier and sustainable nutrient cycling regimen. Until that day arrives, we should be careful and educate ourselves enough to be successful, or just not attempt carbon dosing.