Joseph Miller, a former student of mine, is a reliable expert on STaM. He created the website KosherKlaf.com and can be trusted on these matters.

Moshe Gantz, founder of KosherKlaf.com, is celebrated by the Arutz Sheva Group for his 40 years of continuous support. Learn about his dedication to the Torah and the Land of Israel.

Ateret Tefillin Batim are certified by the Badatz Edah HaChareidis of Jerusalem. Each pair comes with a safety code and an anti-fraud holographic sticker which can be crossed reference with their agency to ensure certification.

Malchot Dovid Straps (Retzuot) are certified by the Badatz Beit Yosef and European Kosher Organization. Each Roll of straps comes with documentation of both letters of certification (Hechsherim).

Zonnenfeld Straps (Retzuot) are certified by the Badatz Edah HaChareidis of Jerusalem. Each Roll of straps comes with a number which can be crossed reference with their agency to ensure certification.

In a letter, Rabbi Michael Taubes recommends Yosef Miller, an outstanding student he has known for years. R' Yosef co-founded KosherKlaf.com with R' Moshe Gantz to bring transparency and education to the world of STAM. They aim to help people know what to consider when purchasing these items. Rabbi Taubes certifies that R' Yosef is a knowledgeable Ben Torah and a trusted source on this subject.

H/T Shmuel Hertzfeld: Removing two names took 30 minutes each of meticulous effort—true dedication. Expert Sofer STa”M: R’ Shimon Zeide.