they are fine if the adjustment screw is set right, turn it up to much and could get problems mine did 47k whilst i had the car and never had 1 problem, but as it was in 2007 diesel tuning was a bit thin on the ground, alot more options around now, tuning box for quick diy power hike or remap for proper safe power hike, after all so much as i had no issues with mine i have heard of people having to much fuel pressure from them and issues arrising