Kung, is your son really interested in the school with the open tryout...that will be your answer. Two years ago, my son thought he was going to play basketball in college. The summer before his senior season he was invited to four college "open" tryouts...he went to none
because of basketball priorities...up to that point two of the schools were calling and writing after that decision...nothing. As it turns out, everything worked out for the best ....but who knows. I later found out those tryouts were indications of "interest but still not sure" opportunites. I say if your son is interested...go, make the best of it.