When these first showed up in the camera store I used to run I though that they were a bit cheaply built. After a closer look it was easy to see that at least externally the economies (plastic self timer lever, unplated plastic top cover and baseplate, ...) were well chosen to not affect performance. I sold a number of them, usually with the 40mm pancake lens.
Time has proven Konica's choices to have been good. TCs don't die on their own as a rule and they are hard to kill intentionally.