Mr. Moto's Last Warning is not the last Mr. Moto - that would be Mr. Moto Takes a Vacation - but it is the one that is in public domain, so that's what we watched on Watch Instantly. (This is counting only Mr. Moto movies starring Peter Lorre.)
This tale of intrigue and derring-do takes place in Egypt, with Moto working to foil a plot that has to do with the Suez Canal - first uncovering, then foiling. He is assisted by upper-class English twit Rollo Venables, played by Robert Coote. This same role in Takes a Vacation was played by G.P. Huntley, as Archie Featherstone. English twits seem to be endemic as comic relief in Mr. Moto movies.
Watching this after Charlie Chan was instructive. For example, the Mr. Moto movie had a budget. There were sets (plural), props and extras. There were real actors, including Ricardo Cortez, John Carradine and George Sanders. So, a real movie. Maybe a B-movie, but not a Poverty Row B. There is really no comparison between Mr. Moto and Charlie Chan.
However, there is a movie poster in Mr. Moto's Last Warning for a Charlie Chan film, title partly obscured by a "Last Week" sticker. It was apparently included as a tribute to Warner Oland, who had just passed away.