Who should wear Rabbeinu Tam tefillin?
The Mechaber writes that "scrupulous people should fulfill both opinions and wear both types of
tefillin, but only someone who is renowned in piety." Someone who is stringent in other areas can wear extra
tefillin without being seen as a showoff. The Acharonim note that today, when many people wear Rabbeinu Tam
tefillin, it would not seem arrogant for an individual to wear them and it is even praiseworthy for someone do so. According to the Gra, however, it is not necessary to ever wear Rabbeinu Tam
tefillin because the halacha follows Rashi and if a person wishes to wear them in an effort to fulfill all opinions, he would have to don as many as 36 other pairs in order to fulfill the many opinions of the Rishonim. Nonetheless, there is an opinion that everyone should wear Rabbeinu Tam
tefillin once in his life so that he should not be considered "a body that has not donned
tefillin" (see Rosh Hashana 17a).
סעיף ב-ג וס"ק יז; ביאורים ומוספים דרשו, 24)