Interesting article
but too brief, and he makes an erroneous claim that the 1925 Scott & Fetzer was the first upright with detachable tools. There were already any number of uprights with attachments by that time, not the least of them the Hoover which had detachable tools almost from the very start. I don't know if the Model O had attachments but I have seen photos of a very similar model to the Model O that had attachments.
Eureka, Ohio, Royal, Air-Way, Bee-Vac, Cadillac, G.E., Hamilton Beach, Sweeper-Vac, Universal, Westinghouse ....... even the Sears Energex all had attachments well before 1925. Just to name a few. Actually, Kirby was somewhat of a latecomer!