I had the same question in the past. (Eccentricity good or bad?) I found out after I bought a high-eccentricity GK. He was an extremely good keeper but he had eccentricity 15. I took the risk to sign him and I was expecting the time of his first mistake, and that came after 3 seasons of 1st team football. I had much lower eccentricity keepers who have done much more mistakes than he has! It's true a high eccentricity GK has an unpredictable style of goalkeeping and this can cost you but also can win games for you. It depends on the situation and the other attributes of the player. For ex. if he has eccentricity 15 and equal or higher amount of decisions and it's a very good keeper don't be afraid to sign him. This keeper was one of the most successful I had in the game, and also the best penalty-saver I ever had!