i visited marimalai nagar last weekend. found it to be mainly industrial estate with small and medium manufacturing units. Ford india factory is located immediately after marimalai nagar in GST road.
water, air quality and chemical, oil smell are some factors to be considered before buying any plot there. however the industries are located in the left of GST road while driving from tambaram. if the cmda plots are located at right of GST road where the railway line passes through then might be the cmda plots are still ok.