I agree on the difficulty in using swivels on the C Class front seats. If you look closely you wlil notice that the front seats are lower than the flooring behind them. If you swivel, the seat is at the same level as the rear floor so your only seating alternative is to stretch out your legs.
Also swiveling the seat involves a lot of trouble because the passenger seat is near to the dash with little adjustment room. Have never tried to install a Swivel driver seat but expect impediments at the steering wheel.
Not worth the installation difficulty, plus $200-300 per swivel. Did it twice and never used more than 4-5 times. Put your effort into more comfortable cushions at the dining table.