They initially had some quality control issues, but MagPul's customer service has been second to none and as far as I know, all have been replaced at no expense to the customers. I've got several of the newest generation and so far they have worked out quite well, but they are prone to cracking if dropped fully loaded, with the feed lips impacting on a hard surface (concrete.) I have not broken any myself, but a friend of mine has broken 4 that way (Then again he could break a steel ball bearing) so YMMV.
I tested a couple out during the filming of the video's that are posted on the forum and they worked flawlessly. I especially like the ease of disassembly/reassembly for cleaning.
Outstanding product for the price. I will continue to stock up on them from time to time.
Erik