The difference is Tesla says you have to pay attention and enforces this, but it can attempt to drive on any street, make turns and lane changes, and navigate to your destination. Whereas Mercedes has a much, much simpler system that only works in a straight line going less than 40mph on certain freeways (so only in traffic).
Isn't this just for relatively low-speed driving, on freeways? IIRC it was limited to under 40 MPH, but on roads described in a way that it sounded like only freeways would qualify. I think there are lots of cars that can drive well under those conditions, though others won't assume the liability.
If your Tesla crashes while using FSD, it's completely your fault, according to them.