I own two, a collapsible 50 3.5 (Industar-50) and a Sonnar 50 1.5 (Jupiter-3), both made in the mid 50's by KMZ.
I like both very much. The I-50 is used for direct sun at around f/11 and 1/250 in general... Obviously, collapsed it's as compact as it gets on my IIIF for carrying... It also has very nice bokeh (!) at 3.5 when focused close, something that took me by surprise, but it's a nice plus...
My J3 is the lens I'm using the most some time ago... When it's not a sunny day, I use it... It's my favorite FSU lens because it's fast and really small, a lot more than I expected... But the most important reasons are: it has low contrast being sharp, with beautiful bokeh, and it's incredibly light... I don't know if all J3's from all manufacturers and decades are that light, but I'm amazed... Almost a joke!
I use it with ISO400 film at 200, and keep an ND9 on it, so for the highest soft light, I shoot at 1/2000 f/1.5, and below that I can use it (until 1/60 without ND) for light up to 8 stops lower, so I can use 1.5 for anything I want, everywhere... When there's direct sun and I want selective focus, I just put it on a light Bessa T body I carry with cap just for sun with the J3, with Acros, and I expose it at 1/2000 f/1.5 with orange filter without metering.
A really enjoyable lens...
Cheers,
Juan