Consensus of opinion was when i was contemplating buying either as i was at the time is that the black ones look like your trying to hide something, which let's face it you most probably are, i.e scabby wheelarches a common comnplaint on T4's at least the chrome ones look like an accessory.....

Below is the advice i obtain re - fitting either/or type
All are better left NOT sealered onto the body and applied with only 3 screws at top middle and bottom so as to be able to be taken off to clean behind at intervals, as dirt, water and grime will build up, making rusting issues far worse, far best to treat all rust on arches agressively with good quality rust remedies, pre fitting and paint with something like cu-rust, over painting with Hammerite to just below the edge of your arch cover, then covering with arch cover, thus keeping them intact, and clean looking far longer, [don't forget to well treat the area around the mounting holes, and don't be fooled sealer them on and it will not be long beofre you have far worse rust up far higher than just your arches....

If it was to of been chrome ones you were going for best to of Vansport via E-bay to purchase good quality chrome against other cheaper versions