https://www.kickinghorsecoffee.com/en/b ... rew-coffee
It was super easy : I used 1/3 cup coffee grounds (medium-dark roast, medium grind) for 1 cup filtered water in a small glass bottle. Then in the fridge for 12 hours or so, to quote Tom Petty "The waiting is the hardest part"

Since I only made a cup I was able to filter it with a normal Melitta cone filter in no time at all.
You can even keep the coffee in the fridge for a week, although I brought it to work to share with a friend and it's all gone

Having had my cup, I would say that I don't think I would use a lighter roast, as it's already pretty light and smooth and I think with a lighter roast you would be left with more of those light floral/fruity notes that I don't care for, but I may be wrong.
I will probably try it with my usual espresso roast next time to compare.
For those who have had coffee from an Aeropress, it's similar in taste, although with still less acidity, a really good cup and very smooth and well-rounded, I don't care for ice coffee so I poured 1/3 of a cup of the concentrate and made up a cup with hot water. If however, you do like ice coffee, then you could simply pour the extract over ice and the metling ice won't dilute the taste of the coffee.
For those looking for an easy way to enjoy a good cup first thing in the morning, this may just be perfect : You brew up a weeks worth and filter it the first morning, then for all the following days, you simply have to boil water to make up your coffee like you were
drinking instant coffee. I know that's what I'll be doing from now on.