I don't own one, but recently saw a comment somewhere to the effect that they flare rather much. Aside from that, Tom A. wrote a nice article in the LHSA Viewfinder a few issues back. It is worth reading, although it will probably make you want one! And in that case, be prepared to spend some $$ as they seem to be enjoying a run of popularity just now--judging by eBay prices. My take on it is that it is a lens you might buy for a retro look in your photos, ot just because you want one--but probably you would not seek one out just for its optical quality. There are better lenses for less money, I'd say.
May the light be with you.