You do not have to really have a refuge or sump for a reef either. I do have one but there is no rule you must have one. As far as the sump and refuge the pros are added water volume which is a good thing and for the refuge nutrient exportation to cut back on excessive nutrients. I dont have any cons except maybe the cost to set one up. I see no reason why a sump will not suffice for your FOWLR
tank. It does not have to be a tank as a good rubbermaid tub will suffice.