This is one of those things where everyone you ask will have their own opinion and laundry list of reasons why they like/dislike, love/hate, etc them.
That said...I would NEVER use them on any of my cars. They do keep your wheels clean but they have their downsides. Rapid pad wear, fade, heavy fade under city or extreme conditions, rubbing on suspension/brake components, and generally pissing off your mechanic are the downside. (if the tech has to take off and put on this extra piece of equipment that dumps loads of brake dust and crud on him that he doesn't get paid hours for...) Plus if the shields rub on anything or cause problems the customer frequently comes back angry with the mechanic. The problem is worse with aggressive drivers, but I've even seen some side effects with "lil-ole-lady" types.
In my experience a bottle of P21S (or any top quality wheel cleaner) and once a week cleaning has done much better in the long run. I'm sure MB engineers had a bigger budget to design such things than the makers of the various dust shields. It works so well stock, why mess with success? If you truly hate cleaning your wheels, plan not to clean your wheels, drive mostly highway miles, drive in a passive/casual manner, etc then the shields might be for you. Bottom line is I have to side with Corky...I can't recommend them despite their popularity.
Hope this helps...Lee