The one I link to above is a PROPER Mercedes service garage, whereas the one you quote is not.
The one I link to is highly recommended and well known here.
The one you quote is only a trading company for hundreds of independant car servicing agents throughout the country. I could not comment on their quality of service.
I am taking my W203 to the one I have shown above next week for a B service. You cant get a higher recommendation than that. And I dont live far from you if I am correct.
Someone will come and take your car away to God knows where and do God knows what to it.
If you really want to use an "under the arches" place, or one of the fast-fit centres, then at least take the car yourself so that you know where it's going.
Otherwise, seek suggestions on here (by searching or asking) for a good Mercedes specialist.
I must apologise, I am finding it difficult sometimes to source the previous threads I need, so I am sorry if I keep asking questions which have been heavily covered.