I have own the Nokton Classic MC F1.4 for 2 weeks and I compare it against the leica 50mm Summicron, 35mm Summicron, 35mm Summilux and 50mm Summilux. Despite the cheap price for the Nokton, I find its F1.4 is not suitable for low light, indoor shooting unless you are working on centre sharp type of photo. The photo are de-focus object anything out of the 30% from the centre. I regret bring this only lens with my M9 on last year christmas shooting my family shots to find out that only the centre person face is sharp and the other person standing beside is all out of focus... On the other hand, on any occasion when I use the Cron and Lux, they are always sharp from edge to corner.
In conclusion, unless you are shooting artistic photo with the intention of defocus corner, don't use them for shot that you need centre to edge sharp and you have one chance to capture the scene at that moment of truth. In fact, I find my Leica X1 do a better job than a M9 with Nokton F1.4.
Nevertheless, I have sold the Nokton at a lost but no regret.