I have had this for several years, and have found it to be very, very good. In fact I am only selling because I picked up a Canon 2x III to obtain faster AF speeds on a few of the Canon lenses I have.
This has been so good to me IQ-wise, and I still wonder if I should keep it. There is a slight contrast loss with this, and a little bit of an AF hit at f8 and higher when you use it with long slow lenses, but I had no issues with the 70-200 2.8. I feel this competes with even the 2xIII, but definitely the 2xII and worth that type of price, I am pricing this at what I feel is a bargain of a price for what all it has delivered for me.
No box, but I am including a very nice padded lens case that you can use with this, or with a larger lens.
Asking $125 shipped and paypaled in the US, and this performs better than Kenko's later models, both IQ and general usability. I have had zero lens issues/errors with this vs some of the newer HDX and other Kenkos. This was one of their prime offerings.
Let's get the IQ test out of the way. 100-400 without the TC with 100% crop
With the Kenko 2x, full view then 100% (actually had to downsize it a bit)
A couple zoo photos with this and a Sigma 50-500 OS, taken with the last 3 pins taped so that the camera would try to AF.
Sports with the 70-200 giving me a 140-400 equivalent