A real time glare would be better applied to high brightness objects. Unless you use hdr exr or similar, a post solution would not identify the hot spots as good. The glare intensity in Octane would keep increasing if the hot spots would go beyond the 255 white. Not to mention how it helps you compose the shot better since you see all those glare effects in realtime.
I'm guessing the Octane solution is so fast because the glare effect is progressive as well. It's not applied instantly in a single frame, but applied progressively over multiple frames, just like clearing the noise over multiple frames.
Notice how it completely changes the picture having the real time glow in the dark scene with the light.