In many MB cars, Sachs Boge are the OEM shock, and are of VERY high quality. For example, the OEM shocks in our 98 C230 are Sachs.
Sachs are generally not much less than Bilsteins price wise. Of course, there are exceptions.
BTW, check Fastlane. Bilstein makes applications for the W124 400E. Maybe your dealer had some Sachs in stock they wanted to sell?
1998 C230 "Black Betty"