My late Father had a 25mm Flektagon lens for his Exakta, which (sadly, with hindsight) I disposed of after his death. I have some lovely industrial interiors which he took with this set-up, and I believe the 20mm version was also well regarded. I've thought a few times that I'd like to get a replacement for my Pentax, if only perhaps for sentiment.
The lenses were from the East German (GDR) Zeiss Jena factory...they seemed to maintain the quality control in these and the long-focus Sonnars, while the 50mm Pancolors could be variable (according to Dad).
Sorry, just realised I'm slightly OT in referring to
the 35mm versions, but I'll leave the post as it gives and indication of the quality of the Jena range. Hope that's OK.