In the west the speedloaders didn't gain acceptance until the mid to late 70s and early 80s. We had to hide our speedloaders in our pockets at the two agencies I worked for at that time. Around 1978 my last department finally acknowledged speedloaders as a good thing an allowed belt carry.

I don't recall Newhall having much to do with speedloader use. I think it was more of a better technology thing as the newer designs of speedloaders worked well and there was no reason not to use them. Speedloaders have been around since before the last century but were most popular from the late 70s until the flow of autos into LE.