Strong magnets for Glaspinwand

I've been looking particularly strong magnets for my Glasmagnetpinwand and also found here.
The cube (each 4 packed in an extra Sackerl) keep the promise.
Unfortunately, one of the magnetic cube was easily broken, is fragmented. Whether the bem Transport has happened ...? or the violent bring the parts apart by my son? I can not say ... guilt was of course not. But because on the table lay a screwdriver that was not there before, I have refrained from the supplier an e mail to write.
So be vorichtig and rather bring apart by hand .... is difficult enough, but they keep on the glass magnetic board and cardboard cards very well.