The medium roast is super juicy with a lot of the coffee fruit flavor coming out. Going lighter, this coffee expresses as overly citric, not especially well balanced, and can easily end up having a drying effect on the mouth, which is not a particularly nice quality for a beverage to have. People who are overly sensitive to ferment flavors should avoid the medium roast as it's the sort of flavor that's wonderful, but rightly causes deep skepticism if encountered on a pre-ship sample.
As for the dark roast, this is one of the lighter dark roasts and I'm pushing it fast enough to get to the high temperatures needed to get the dry distillation notes that dark roast drinkers are looking for while also preserving some of that fruitiness (moving it more to the aftertaste) and sweetness that I like about the coffee. That combination brings a complexity to the flavor often missing from dark roast coffees, making it an excellent gateway to the dark side.