This is designed for "fast" and "high power", but not for efficiency: it's not a combined cycle plant.

Yeah, its totally inefficient - according to Wikipedia a simple cycle gas turbine can be up to 43% efficient - with a combined cycle (you boil water with the first stage jet engine exhaust and then run a steam turbine off that) it can get up to 64%.

So like this there is possibly about 20% of (a lot of) energy/fuel just wasted. You can get even better, running something like a city wide district heating off the waste heat from the steam turbine - potentially reaching 100% in the sense that people get heating, warm running water or possibly also process heat for industrial use.

Or you can do none of that and power a datacenter of questionable utility with it at about 40% efficiency. :P