Sdbutler is right, cheaper drilled discs do have a tendancy to crack over a period of time.
I have even heard people say that the Irmsher ones fail.
I think it all depends on how you drive and the quality of the items, i run genuine Saab Grooved items and they are one of the best disks i have used. With non named discs like above i may expect them to fail after a year.
All depends on your budget really. Mintex / Black diamond / Tarrox and others are all good but you will pay more.