Works Great
This converter does what it is suppose to do with very little image quality lost. You do lose one stop of light though just like any other 1.4 converter. I just take it off for the last half hour of the day if I need the extra stop. Like I said it works great with my 40-150=80-300 2.8 pro lens. that gives me about 420mm with teleconverter. Also seems to be very well made and have not had any auto focus issues with it.
Pros: Fast focus, small
Cons: None