I recently purchased the pre-asph 35 Summilux and while I am still getting acquainted with it, I liked what I saw from the lens from other users and no longer seek the pre-asph v4 35 Summicron. The pre-asph 35 Summilux is very sharp when stopped down and has a unique character when wide open. I like this combination because it saves me from having to carry an extra lens. Also, even though you don't necessarily need a super fast lens at the 35mm focal length, for my purposes I could use the extra stop because I often shoot my pre-asph 50 Summilux wide open in hand-held situations that call for 1/4 to 1/8 shutter speeds--still possible to do, but why risk motion artifact? I never really considered the slower or sharper 35mm lenses because I did not necessarily want sharpness all the time.
The key thing is the size. While being a fast lens, it is remarkably small. Very useful as an all day carry around lens with wide and narrow depth of field when needed. The pre-asph Summilux is a unique lens and is much maligned, yet it is curious to see that not all that many are available for sale at one time. It is definitely a low production sleeper of a lens and not many people talk about or use it (similar to the pre-asph 90 Summicron), but it's a great one when you "discover" it for yourself.
Regarding flare, I shot about 100 frames with it on my first day, and I only got it to flare once. But I almost anticipated it because there was heavy backlighting and reflections from the sun. I will have to shoot it more extensively at night with point light sources before I comment on its performance under those conditions.
