I've used the DDM slim ballast kit on my previous car and my current car. On my old civic i had the 35w kit with no harness for about 3 years and it worked great and never had issues. I had it on there the entire time i owned the car and no failures. Now on the other hand i baught this same kit but in 55w on my WRX. Heres where it gets kinda interesting. I used the wiring harness for this one and ive had nothing but problems. One ballast would go out, so i'd swap them around from the left to right side. This would fix it for maybe a couple days then the same thing would happen again with. So i decided to remove the harness and see if it would work. and what do ya know, it did work! So far ive been running it for almost a year now and i've had NO issues at all. Mind you these are the same ballasts. Weird.
Overall all, for the money i approve of them and would recommend them.