Just received today the Kenko 1.4X Teleplus MC4 teleconverter which turns my ZA 135 into an 190mm f/2.5 lens. Took a few test shots from my balcony at f/2.5 and f/5.6 to see how it behaves at infinity.
You can find them here.
I found the lens/converter combination to be sturdy and balances well on the tripod. The exif shows the correct focal length (well, it says 200mm but that's close enough) and aperture. AF is accurate and not as slow as I was expecting. The IQ is also surprisingly good. The results WO are unusable for landscapes but I wouldn't shoot landscapes WO anyway, even without the converter. At f/5.6 the IQ improves a lot and the results are quite OK imho. I didn't try smaller apertures (my bad) but I would expect the IQ to keep on improving further (optimum aperture for the Sonnar is f/5.6, or f/8 with the converter). I think the combination is very usable WO for close distances but I have to take more photos to test it.
PS: I think the first 2 frames have some AF problem. The other 2 with a slightly closer distance look much better.