Well since this thread has been revived anyway I thought I'd give my input.
I ordered a few of these a while ago, and my experience is that they are absolutely terrible. I don't know if I got a bad batch or something, but they were nowhere near the quality of the official sticks.
For one, the sticks were too short. The rubber padding on the top actually made contact with the controller when I moved the stick all the way so I had to put a little piece of paper inside to raise it up a little bit.
Also, the quality of the top of the stick was garbage. It actually wore down after only a couple hours of use.
Not only that but it is put together very poorly. The rubber cap came off almost immediately after playing on all but one of my replacements.
All that said, other people seem to like them so maybe I got unlucky. If you really need a replacement cap then the Nunchuk cap fits perfectly and is much more durable. It's raised up higher than the Gamecube one however so it might make it more difficult to be technical.