The only drawback I see with this lens, is that it can't be used on full frame Canon cameras. The rear element would hit the mirror when focused to infinity. Another minor complain is its yellowing elements for the earlier versions. But man, what a joy it is to use this lens. In terms of workmanship, it has to be one of the best, regardless of price. Not quite the same as Leica, but darn close. This lens, like all early Takumar lenses, is a dream to focus. You turn the focusing ring, and it feels like a butter knife going through a brick of warm butter. Great built quality is nothing if the optical quality sucks, but of course, the Takumars are also known for excellent optics.
After decades, the SMC 50mm f1.4 Takumar is still as close to, if not better some of its modern counterparts in terms of image quality. In terms of build quality, it's beyond compare. My 50mm f1.2L lens is not as well built as this lens. The bokeh on this lens is sweet and delicious. If you can have only one affordable 50mm f1.4 manual focus lens, this is a prime candidate. I have not had any regrets with any of the Takumar lenses I have own, not even the one with fungus.
Iris -- Canon 10D & Super-Multi-Coated Takumar 50mm f1.4. Click to see larger.
Megan (2005) -- Canon 10D & SMC Takumar 50mm f1.4.