If your priest celebrates the Traditional Latin Mass, then he should probably have one, and would more likely appreciate it. I would not worry about telling him how to use it–he is the priest, and if he has learned the rubrics of the EF, then he can easily learn when and how to wear a biretta. In other words, it’s not your place to tell him when and how to use it, especially since you really do not know, yourself.
However, if he does not celebrate the old Mass, he may not appreciate being given a biretta. If he is into elaborate vestments, courtly and/or Roman things, he may like it. If not, he may not, since one rarely sees birettas in the OF.