In response to the concerns articulated by Benephraim and DrYidd as to why all the Gedolim did not accept the opinion of Rav Moshe Feinstein zt’l concerning this issue, see the most recently published volume of responsa Shevet HaLevi (vol. 11, Y.D. section 198), by Rav Shmuel Halevi Wosner zt’l (referred to by many as the Posek Hador) where he testified that “With regard to shaving machines…it was agreed by all the Geonim…that there is no difference between [using] them and [using] a razor… The Gaon R. Moshe Feinstein sought to make a distinction between today’s [shaving machines] and a razor and advanced a theory [in justification]…. That theory is not correct and has not been accepted (אינה נכונה ולא נתקבלה aynah nechonah v’lo niskablah).” [It is important to add that Rav Wosner personally discussed the halachah of shaving machines with Rav Moshe Feinstein during a face-to-face meeting between these two Gedolim which took place in 1978, during a visit by Rav Wosner to New York (on behalf of Vaad Mishmeres Stam). For further reflections by Rav Wosner regarding this visit with Rav Moshe Feinstein and their exchange regarding shaving machines, see Rav Wosner’s revealing letter dated 9 Nissan, 5738, published in Hadras Ponim Zokon (third ed., miluyim to Section 2 ch. 1, p. 729).]
Similar sentiments were expressed by as great and as universally accept a Posek as Rav Shlomo Zalman Auerbach zt’l. In the 5778 issue of Agudas Yisroel of America’s Am HaTorah journal (5:9), Rav Pesach Eliyahu Falk (Rov in Gateshead and author of responsa Machzeh Eliyahu and many other halachic works) testified that he personally heard from Rav Shlomo Zalman Auerbach zt’l how he rejected the reported reasoning of Rav Moshe Feinstein zt’l to be lenient regarding electric shavers.
Indeed, many Poskim wrote clearly that one may not rely on the Igros Moshe regarding shaving machines. The Poskim include the Steipler Gaon in Orchos Rabbeinu vol. 1, Hosafos Chadashos p. 38.; Rav Elyashiv; the Debretziner Rov, author of Shaalos u’Teshuvos Be’er Moshe, in his letter published in Hadras Ponim Zokon p. 22 (where he writes that he does not believe Rav Moshe Feinstein zt’l ever issued such a heter); and Rav Moshe Sternbuch (in Teshuvos v’Hanhagos, vol. 5, section 264) and others.
For additional reasons why the Igros Moshe’s position regarding shaving machines was not accepted by the Gedolei HaDor (including a responsa with the Haskama of Rav Chaim Kanievsky shlita), see the recently published work Authoritative Responses to Common Misconceptions, chapter 12 (which is available through Amazon and can be viewed at no cost in the publications section of the koshershaver.info website).