None of the vintage Summicrons is a good value on the used market relative to their performance, and the version IV is the worst offender in that regard. It's not a bad lens wide open, but every CV 35mm lens I've tried (1.7, 2.5, 1.2) is better. You're paying a real 'internet-hype' premium for it (bokeh king!) and getting a lens with middling build quality for your troubles. I had to send mind to Sherry twice to have the loose barrel fixed, then finally broke down and did it myself the third time it happened.
The lens IS a perfect size and handles wonderfully, but regarding optical performance, there are better buys out there. Heck, at today's prices I'd recommend the pre-aspherical Summilux over the Summicron. The 'lux is just as good as the 'cron at f2.0 - maybe better - and you get a unique look at f1.4 to play with! 🙂