The Four knights: Scotch variation is very rare and occurs in less than 1 in 1000 games. From the data, you can expect that White will have a very high 55.07% chance of winning, while Black should only have a 44.93% 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.