So I got
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working for my Rift S setup and I must say that it is pretty awesome. I kept it at 0.75 for both renderscale and sharpness and it does really improve quality / FPS (depending on what you want). I also noticed that the text get's slightly more blurry than without it but when you play a scene it looks great. If I would be twiddling in VAM creating stuff I'd probably set it 1.00. For playing scenes 0.75 is awesome however as a performance improver.
Don't be an idiot like me btw, and make sure that you copy the .dll file to VAM_Data\Plugins. If you copy it to the root directory of Vam it does load VAM, but it keeps hanging forever. Took me a few hours to find out that I copied the .dll file to the wrong directory.