For comparison, I've got a California Lightworks Solar Systems 275...it retails in Canada for about $585. A comparable HLG is about $450 and you have to build it yourself. My lamp has a five year warranty, that allays any fear I have of having to lay down cash to fix or replace it. I've only got a thousand hours on my lamp, but it's worked well so far. For my money the difference was worth the reduced risk. YMMV
I'm not great at interpreting all the lighting literature, but I'm pretty sure the total output of the lamp I have, is more targeted to the red and blue spectrums, whereas there's a lot of output in the middle range, that the plants don't really use, coming out of the HLG lamps... that's my understanding, so "efficient"? I'm not so sure.