Canon EF tele extenders III

I have both of Canon's new tele extender III teleconverters in hand, I've shot them with several lenses, and I'm preparing a report on them. I'm testing them with the EF 135mm f/2L, the 70-200mm f/2.8L IS II, the 70-200mm f/4L IS, and the 300mm f/2.8L IS.

At about $499 each, Canon clearly considers them serious tools.

Just released in January 2011, the new EF Tele Extenders promise to improve image quality over the two earlier generations of teleconverters, which have never proved satisfactory to me on high resolution digital.

Do the new converters offer good enough quality to really not feel like a serious compromise? Remember that performance can vary lens by lens, and can vary on a zoom lens with the focal length. So the answer might vary, but so far it looks like the results are very good in general.