Also note, it happens that this trim has dark coloring at the edges in the picture, so look at the lower corners for a more precise sense of the light fall-off. For 2x TC, I've only bad news. The following is an example of how it really looks like when used with TC-200. The overall contrast of the image is low. The linked photo page is an example.
Many people are concerned about the lack of tripod collar in the lens.
Their concern is that the lens could damage the camera's lens mount. My concern is the tripod socket of the camera. But someone comforted me that the even the nightmare happens, it is quite easy to have the camera's tripod socket replaced. Also, big and heavy. Forget about teleconverters unless you already have TC-14B which is bought not solely for this lens.