I decided to give it a whirl. I used the same ratio I would for cold brew coffee. About 1/4 of a cup. Sometimes more, usually a bit more because I'm not that precise and I don't bother to smooth off the top. I added raw milk because that's what we drink. I had read that milk can bring out the bitterness faster than water for all sorts of science reasons which I am not going to look up again. The posters on Reddit left it for 10 - 12 hours like regular cold brew. One tried different times and said an hour was too little, 12 was too much, but for him 10 was perfect. I didn't know if the milk being raw would affect it or not so I decided to try after 5. For me 5 was perfect. 10 would have made a bitter mess.
Then I used a metal filter to drain it into another mason jar. That was a bit of a pain. The grind was not as course as I would have liked, because I forgot to check the settings first. I didn't want to grind more, so I went with it. Because the grinds were a bit too fine the filtering was time consuming. I had to keep stirring it to keep it moving.
The result? Something really good. It looks like chocolate milk but tastes like coffee, some bitterness, but not overly so. I don't use sugar in my coffee and it was fine the way it was. Add sugar and I think anyone would love it. Even people who don't normally like coffee. It would make a great ice cream or milkshake and I think adding it to iced coffee would be fantastic. Going to try that tomorrow. Adding milk without diluting the coffee flavor. I'm going to make this again. It's really good.
My friend Sarah saw my photo and made some herself. She used traditional milk and 5 hours was just right for her. Luckily she had fewer problems filtering it. She was happy with her results. And she had a nice bottle from IKEA to put it in.
In short - try it. I think you'll enjoy it.