Here's a direct comparison, so you can judge how good it is for yourself. All three use my difficult orange test case - RGB(255, 128, 64)

#1 is no correction
#2 is anti_GC the incoming color, do the diffuse+specular effect, then GC the result
#3 is take the incoming color AS IS, do the diffuse+specular exactly the same, then HSVETM the result

I'm using the HSVETM exponent 1/2.2 - 1 = -.545454 here so the luminance change is approximately the same.

There is a small difference in how the specular renders. Other than that, the GC and the HSVETM are very similar.

---

Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)