This is my second copy of the lens. I purchased locally when I read that some samples had problems and was glad I did as the first copy was decidedly soft on the entire left edge from top to bottom. The second copy is extremely sharp over the entire frame wide open and improves only very slightly when stopped down.
After performing a microfocus adjustment, part of my resolution tests were to check for focus slop by alternately starting the autofocus from the near limit, then the far limit, etc. There was no focus slop at all, the results were identical
I'm not a working pro and take very good care of my equipment, so I am not at all concerned that some plastics are used in the construction of the lens, although the plastic filter threads may need some care. But the plastic threads could be a positive for filter use as they may be less prone to seizing if a filter is over tightened. Brass filter threads are of course ideal, but most filters have aluminum threads.
I like the locking of the lens hood with the latch button, a very nice improvement.