I had 2 boxes of the Dunhall, premium and experienced the same burning taste rather quickly, perhaps 30 drags. However, from my experience, it's not a faulty carto. I think the problem is, the Dunhall's, for whatever reason, are not filled with enough juice.
I say that because when I got to the burn taste point, I would refill them with my own special mix, which I won't name, and they were fine after that (at least for a few refills). However, if you take any more drags after that first hint of burnt taste, then the carto is trash.
But I also think once you get even that first hint of burnt, it will affect the carto in the long run. I think that's why I only get a few more refills before things start changing for the worse.
I don't order Dunhall cartos anymore due to that. I will use & refill the Kant cartos and also just use blanks. Mainly because I haven't found a better tasting juice than the stuff I mix now.