Summary: I can think of only two reasons not to buy this lens. One is that you own a pentax fa 50mm f1.4, which weighs about twice as much (but costs about the same per gram), and which gets very good reviews. The other reason is that you own the pentax da* 55mm f1.4, which means you don't mind extra weight and you don't worry about leaving an inheritance to your heirs.
Excerpt: Just bought the new K-3 here from B&H and it came with this lens. Initially thought this would just be something Ide just resell, but ended up really liking it! The Boahka is smooth and possibly even better than my old FA 1.4! Still can't believe how well this cheep lens preforms! As stated by many before, the autofocus is LOUD, but quick and spot on.
Pros: Fast / accurate auto-focus, Great Colour Rendition, Nice Bokeh
Excerpt: I would totally recommend this over the older FA 50mm f1.4, having owned both. This is sharper, has fewer color issues, less flare and smoother bokeh, for half the money. It even has a superior manual focusing ring! The only drawback is that it's probably not very rugged.