Reply To: Type of Tefilin you wear

historically, the actual debate between rashi and rabbeinu tam was not which are the only kosher. cause then the question would be, what did people where 100 years before? the question mainly was which is the main pair type. almost everybody wore both. rashi said his was the main, to be put on first. after that most european decided one pair, rashi, was enough. sefardim mostly wore both, some st one time together.

the ari zl came ad said both should be worn, rashi first. so chasidim all wear both. chabad wears both after bar mitzva and some other chasidim do that too. all chasidim wear both after getting married.