My father, who is a professor of Chinese, has the following to say:

I have been using QIM for about a year and find it excellent. The characters are clearly displayed, having frequently used characters movie to the front is very useful, and I have not had any problems with it. On the contrary, the change of the Apple fonts that came with OS10 is a disaster, many common characters are not included, and the range of input methods are strange indeed. Thank goodness for QIM.