Does this method to get Portrait Mode on the S9 actually work?

You don't need that. There's selfie focus and selective focus built in on the S9 for blur. I know because I have the S9 Exynos.
 
So I went to the store and tried out the Selective Focus mode. It would not focus properly 9 times out of 10. Even when it does, the face is in perfect focus when I took a shot of a man standing but the hands are blurred out. I tried a few shots and they were all the same. It also requires you to be very close to to object I couldn't see myself dealing with that on a daily basis so I ended up getting a Note 9
 

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