http://www.pentaxfans.net/thread-146196-1-1.html
By a Taiwan Pentax user and the above post is in Traditional Chinese.
Most of the test pictures posted are self-explanatory, though. Just browse through the page and inspect yourself and find out all the differences, if you can see any!
Btw, I am impressed with the IQ of this converter, at least on a cropped sensor. This TC is rather expensive, anyway. If it is confirmed to be FF compatible, I would not hesitate to invest. But as all the other Pentax stuff nowadays, not to even mention about their rareness and the lack of new models (there are only a few each year), the problem to buy is only about the lack of faith, frankly. It is all because we cannot see the future nor the direction of the brand, which has been rather unclear for years now! >:-(