I was thinking of getting them too. My 8-holers are chrome and MAN, do they show the dirt!
I figure they are safe since they do have the slotted cooling vents. A tip for others considering the purchase is to take a look at the design of your factory wheels...if you have very open wheels (like the MLs), I probably wouldn't get them. The factory put them on for a reason, and it's probably because they need all of the cooling they can get!
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car