Interesting that you posted this right now, as I am currently running a roll of film through a Pentax ME (first time) and a 40mm 2.8 (first time). I haven't finished yet, so don't have a verdict, but I would say my feelings match up so far with those of the author of the article.
In some brief testing on my DSLR the 40mm wasn't particularly good, and my first thought was the same as the author, why not just use the 50mm as it's almost the same size and really good? But the 40mm focal length is a little bit better in my eyes, and I can fit the camera and the lens in a little fannypack
We'll see how the scans look after I'm finished.