Not disputing anyone else's experience but my 8 year old son and I ran the new Jconcepts ball cups indoor club racing last week with zero issues. They move freely, have very little slop, are stiff enough and none popped off even though my son spent the first hour of practice trying to figure out the the triple. Also, given you don't need to take them on and off much due to the ball stud access holes I think they will last a while.

No ball cup design is 'perfect' -- there always is a compromise among a variety of considerations. The RPM's are very good also -- but I have from time to time popped one off, especially on my B44.2.