Some people speculate it probably has surpassed 1 million units if combining the total sales from SW1 and SW2 versions of the game. However, its certain to not have passed 2 million units as of the latest may financial report.
Like some people on this sub, i dont like most of the artistic changes the mod does for the game. But on a technical level, its lighting system is superior to the one in the base game. Thankfully, you can adjust settings like color, luminance, skyboxes, etc... to return the game closer to its original look, while maintaining the positives of the lighting engine mod.
The forest of the fallen giants is one of the biggest examples of this. In the original, baked mod, its all grey and dark bluish. When the art style was clearly going for a sunset wasteland kinda look. So i returned it to that the best i could.
Majula was the hardest one to find a balance in the colors that i was satisfied by. In the end it ended up looking more like vanilla ds2 than the SOTFS version of Majula.
This is the regular lighting engine mod you can find on nexus mod btw, not the path tracing version.
Link in the comments if anyone is interested in downloading my settings.