You need to check the handbook ... see if there are towing limits given.
When type approval came in manufacturers stopped certifying a lot of models that were 'unlikely' to be used for towing, because of the cost of the process. It's illegal to fit a towbar that isn't type-approved to a car registered from 1/9/98 onwards.
I did check the Witter website originally - didn't see any listed for the W208. That's not necessarily significant as I know the R129 is approved for towing, and they don't list one for that either (not enough demand, presumably!).