This system does not do OBD I, but if you will call the 800 number found on the website and ask for Tom, he can tell you what to add to your system to make it work.
Yes, mine only does generic codes on everything except Toyota. I originally bought it for my wifes four runner, and it has ALL propietary stuff for Toyota. Unless they have added it later, I don't think they have any enhanced product for MB.
The generic codes will got the job done on most any problem.
Have a great day,