Co-incidently, I found two boxes of the BMS budget Durhams in my store cupboard. They are actually Best Sub J.S. Coated mugs and I found them to have zero defects (almost)! Maybe 2-3 out of 72 were not suitable, but that is impressive. These are very straight mugs, the 5013 have a long thin dent around the circumference about 5mm from the bottom of the mug preventing full top to bottom printing.
The only issue with this BMS mug is that I don't think the coating is up to much. It needs a longer time in the oven, half the mug can look faded and full colour prints aren't transferring very well even with 3 minutes extra in the oven. The colours lack contrast and look washed out compared to the 5013 mug. I reckon maybe the coating is a bit thin in places, but right now I've no desire to investigate. The search continues for an easier to print mug.