If you want to practice cupping by putting ground coffees in cups and pouring water over them; any grinder will do. The essence will be to use the same roast level for each coffee, and learn how to describe tastes and smells.
In commercial cupping, grind retention is not that important. Each coffee is brewed in three to five cups, each ground separately, and before any of those cups are ground, a first cups worth of coffee is sacrifice ground to clear the grinder of other coffees. Multiple cups of each coffee are brewed for cupping because there are usually lots of tasters, and because the uniformity of the coffee needs to be checked. When doing three to five cups of three to twelve different coffees, grinding one cup at a time; the requirements for the grinder are speed, absolutely repeatable grind settings, and consistent grinding with only one cup's worth of beans, about 8 grams, rather than a hopper full of beans. These requirements are only fulfilled by bulk grinders, like you see in supermarkets.