The bulbs were an easy fit on my Discovery 2 providing excellent light. I only hit 2 minor snags: the instructions highlight to set the bulb holder blade vertical but fail to explain that they can also be 180 degrees out. On my the H4 I bought I worked out that the wires need to exit the bulbs at the bottom as a guide. Getting this wrong results in blinding on coming traffic with pools of intense light, getting it right provides a good spread of high power light across the whole reflector; the factory rubber galoshes on the back of the bulbs do not fit the leds due to the size of the cooling fans. I have left mine off but this may present an impact on bulb longevity in the long run.