If I am not mistaken the 28/3.5 M was sold only in non-U.S. markets. In the U.S. you could get a 28/2 or a 28/2.8. The differece in price between the f/2.8 and the f/3.5 was not significant enough in the U.S. for both models to be offered.
That could be. I did have one and am sorry I sold it. I'm going to pick up another or an SMC Pentax version one of these days to replace it. I have the 28/2.8-M now, and it renders nicely, but it just isn't as sharp as the 28/3.5-M to my eye, and that seems to be a pretty typical impression of it, from what I gather. I still have my old EBC Fujinon 28/3.5 I bought new 35 years ago, and that's nice and sharp, a very nice lens, but I lose auto diaphragm with it adapted.
I do use a digital device in my photographic pursuits when necessary.
When someone rags on me for using film, I use a middle digit, upraised.