The Scotch: Relfsson gambit ('MacLopez') is extremely rare and occurs in less than 1 in 10,000 games. From the data, you can expect that White will have a high 66.67% chance of winning, while Black should only have a 33.33% chance of winning. Because of the fact that most players probably have never seen this opening, and that Black has such a low expected chance of winning, it may be well worth it to keep this variation in your back pocket. Since as White, you should have a significant edge and will probably catch your opponent off guard.