Cantinflas has good movies but this isn't one of them. The jokes aren't funny, there is no plot, no moral, and on top of that, the movie title is misleading. Maybe Cantinflas was at a point where he would be successful whatever rubbish he did because he was famous? I can't be sure, but his otherwise hilarity-ensuing cleverish loquaciousness is just a shadow in this film with a lack of luster and funniness.
If you want to see a good Cantinflas flick, start with the first one, dubbed "You're Missing the Point" or better dubbed "There's the Rub", where his true character comes alive. Some of his later work is also worthy of watching, so it may not have been a popularity issue but a mere dud. Whatever the reason, "A day with the devil" is a waste of time for anyone other than a Cantinflas fanboy.