Curious why R. Adler would have used the Sephardic spellings "matzote" and "mitzvote." I thought maybe he was following the spellings of his correspondent, but the "Elm Street Congregation" evidently would have been B'nai Jeshurun, which was NYC's first Ashkenazi congregation. It had broken off from Shearith Israel in 1825 davka because its German and Polish members resented Sephardic control. And yet it still had a "Parnass" in 1850, which may indicate a lingering Sephardi influence.
By 1850 very few European educated Jews would have written a Hebrew word using the Ashkenazic transliteration. Besides for that, there was also the Sephardic influence in England, and still lingering in the US. Basically, the idea of "Matzos" in English probably seemed very foreign, is my guess. It is also possible that this is Leeser or someone else, but I doubt it. I've seen some of the Leeser-Adler correspondence, in Rabbi Adler's own hand, and I can double check how he writes.
Did he pronounce a cholam as "oat", or is this an artefact of the transliteration?
Certainly an artifact, but if I am not mistaken in Hannover, where he was from, they pronounced the cholam "au" (I think in Southern Germany they pronounced it more like "o" as in "oat.") It is however entirely possible that he personally worked on his pronunciation to make it sound more English, and either pronounced it "oa" or tried to.
there is a picture of the machine in grinstein's book. also a later picture from late 1850s with mashgiach (mj raphall?) in the background.