I have been using this myself also since I stopped taking finasteride. The consensus is to simply brew your own coffee like you normally do and store it in a bottle in full strength, do not dilute or mix with anything else. Then use it like a hair conditioner , leave it in, towel dry.
I do get more body and volume to my hair, no doubt about that. Some say coffee can be used as anti androgen and counter DHT on our scalp, I haven't found too many studies about that yet. We shall see if this stops further hair loss for me.
BTW, I am also using topical minox.