Good Day Fellas,
I have heard so much and I have also seen couple of coffee paintings but I had never attempted it untill now. If I would be giving my sincere comment about using coffee as a medium for painting, I would say it isn't far from using the watercolour medium at all, it's so fun for me but it's just a single colour and I think that's the only disadvantage that comes with it in terms of comparing it to watercolour.
Kindly share your thoughts as comments below, I'll be glad to read and reply them all. Thanks.