This older normal lens can be bought quite cheaply as there are so many around. I already had a good Rikenon F2 50mm, but decided to try this native Pentax also. There is not much to lose with its price.
Here's an example picture today, as the sun came up after some very rainy and bleak weeks.
After some experimenting I think that Pentax M 1,7 50mm performs about equally with Rikenon in short ranges, while the latter would seem to offer some more resolution at long ranges. The Pentax feels certainly as better built precision instrument, as it is metal, and is good looking.
The plastic Rikenon functions not so smoothly any more.
The next lens I'll probably be after may be the Sigma 70mm Macro, which has got many good reviews. I long the sharpness that I got with Tamron 90mm Macro (for Canon), that i sold lately. Maybe Sigma matches it and gives also some more angle.