I haven't seen the dozen or so film/Tv versions of De Filippo 's popular 1946 play but a case can be made that this 1951 adaptation which he himself directed and starred in should be more well known, in comparison to the 1964 remake with its bigger stars ,its use of color and its several Oscar nominations.
The comedy is first of all based on the fact that the businessman and the ex prostitute who tricks him into marriage are both getting old and want to make a definitive statement as they head into their last years. (The prostitute's possible death halfway thru the story is a main plot point.) In the play the characters were both around 50 and here Eduardo and Titina were actually both around 50 themselves.(By contrast when the remake was shot, Mastroianni was only 40 and Loren was only 30.)
The 1951 version is also more realistic in that the characters are less glamorous than the decidedly more photogenic performers in the De Sica version .It could in a way be described as being closer to Neo Realism.
My favorite scenes here involve Eduardo's sizing up the three young men who Titina has foisted on him, her illegitimate sons one of whom she claims she had by him, but she won't reveal which. He checks out different aspects of their behavior to see which he is possibly related to, at one point testing their singing abilities since he fancies himself a fair singer. (The irony is that there is a real musician in the cast, future "Volare" author Domenico Modugno, but he plays the lawyer, not one of the sons.)
The strongest aspect of this moving and charming film is as a showcase for Eduardo's sister for whom he wrote the part of Philumena and who played it on the stage.She was a talented lady often reduced to supporting and somewhat shrewish roles so here she really gets to shine.