I don't know how they would work on a model but in full scale, a roller furling genoa or even a jib, is never used for racing because they are cut different than racing sails and sag too much. Because of the roller furling the genoa sags and cannot point as close as a racing sail.
In a model race, one must tack extremely quick in order to stay ahead of with the fleet and I doubt any mechanism could be developed to roll the geona in and let it back out fast enough to keep the other boats at bay, at least not at a reasonable cost. The cost benefit question still comes up since a large main and a regular sized jib can be the most efficient combination.
With a genoa, one would have to use a shorter mast because of the increase in sail area, or install more ballast and possibly lose overall speed. Genoas are at their best when off the wind on a reach. No, a jib is not a genoa.

3dbob