I did a quick read in the article and while it gets in conclusion that induction has only 15% efficiency compared to a typical open fire, it is considering also the conversion of heat in energy by a thermoelectric (that is the actual inefficient process). While I understand the point of the article this is not a valid general conclusion of the efficiency of induction cookers, since you can have much more efficient ways of producing energy.

Induction cooks by themselves are very efficient in converting energy to heat (90% efficiency, according another claim in the article).