It’s a tricky question, once you have played the cheapo non brand ones and the good ones you’ll be able to “feel” the difference. I used to have the same question, after owning a few JKAs, I can tell right away if a kendama is good or just poorly made to make quick money.
It’s something probably not noticeable by a complete beginner who is currently learning basic cup tricks, but once you get to a certain point you’ll be able to tell right away.
If you are starting out, get a JKA, either Ozora, TK16, or Shin Fuji, you can’t go wrong with any of them.