It works fine for me. There must be something else going on with your setup. Are you sure that hardware raytracing is enabled and that your GPU supports it, along with SM6? Megalights requires them. Also, are you using a post process volume to flip it on and off? Make sure it’s set to unbound to include the entire scene. Lastly, make sure that the graphics preset level is high enough. Probably has to be on high or epic to be enabled.
Here’s the constructor script I tested with that randomizes some values:
10x10x6 grid of lights: 85fps with megalights enabled, 23fps with it disabled.