Just out of curiosity -- did you read the article I linked atop my previous post? I go into great detail there on how to do cheap macro, really.
No, not all TC's suck, just the affordable ones. It's like this: There's 4 types of TC's that can be used on your Kx: M42 screwmount (manual everything), PK-M (manual everything), PK-A (auto aperture control), and AF (autofocus and auto-aperture). Each of these are best suited for lenses with the same mounts.
M42 and PK-M TC's are almost always a crapshoot. They extend the focal length (for better or worse, usually worse) but you must do everything manually. PK-A's allow aperture control, which is mighty handy, but most simply don't have superior optics. And any lens problems are magnified. That leaves the AF's; the best are very good and costly, are matched to specific lenses, and won't work well with other lenses. If you're a serious birder with a budget for high-end glass, they're great. Otherwise you'll usually get better IQ by cropping the image.
NOTE: I just bought (CHEAP!) a good M42 TC that's matched to a specific lens. Now I just need to find that lens...