I have used the Mercedes jacks on 4 that I have or do own and never had a problem. Wheel chocks or one such item may be good to add stability, but if you put the car in Park, set the emergency brake On -- and jack up the car properly,there is no real problem! It seems to be more of a case that people who are not used to the design think there is something wrong with it because it is different!?

These jacks work just fine in any instance. If you are using the American type of jack with a long base, it can have the same problems on a soft surface that the German one can -- sinking into the surface. Also, the American design has relatively weak side bars and can twist and collapse if the weight is not properly distributed. Both jacks are fine for their purpose.
Just learn to use them as intended.

__________________
Ben Harrison Carter
1999 Mercedes ML320 87K
1992 Mercedes 300CE 89K
1995 Corvette 29K -- Sold Dec 09
1989 Mercedes 420SEL 99K -- (Sold 4/08)
1968 Mercedes 230S (106K) (Sold 9/06))
1976 Mercedes 450SEL 130K (Just sold - 06)
1961 Mercedes 220Sb (sold years ago)