Jamieson,
I have the Nokton 1.4 (35). Build-wise, it is the nicest little lens you have ever seen. Feels really good in the hand. It is sharp from 2.8 on. Below 2.8 it is ideal for softer portrait work. Renders colors rather cold as compared to my C Sonnar that in my experience is neutral. But no complaints about any of these. Getting to my complaints now: very noticeable barrel distortion, and some focus shift. The focus shift, again, you get used to it and compensate for it, specially on a 35. The barrel distortion is unnerving even though you can hypothetically fix it in photoshop. I have noticed that the distortion is not a perfect Gaussian distortion, so photoshop does not account for it accurately. In comparison my Jupiter 12 has less distortion! Nokton has some light falloff in the corners as well (vignette) but I find it cute. I'd say the same level as Jupiter 12, but less harsh. I can send you good test shots if you want. Hope this helps.