I've purchased the comprehensive & extended Starmark warranties for both E500 and E320 Coupe.
A couple of years ago, the E320 Coupe had sunroof problems and apparently needed what amounted to very expensive & time consuming r/r. According to MB Factory Authorized Service here in SF, this sunroof repair was not covered under Starmark (sunroof motor was not the culprit).
After this experience, I reviewed Starmark under close scrutiny, and did not find the failure specifically covered. I did surmise though that Starmark offered a great value in covering the "major" mechanicals.
Also, I find value -on most jobs- having factory techs diagnose & address repairs together with a warranty on the parts, labor, & repair going forward.
If one can forge a good solid relationship with the advisors and techs and have your machine well cared for, it makes the pricing and busy scheduling more palatable.