Non multicoated ones are more reflective, less light passes thru and degrade the image quality, just try to look thru a pair of multicoated glass and a non coated glass to light sources and you get the picture..
MRC is Multi Resistant Coating. Coating which is used by German B+W filter, which is famous because its strength (easier to clean than other brand). Other brand may not allowed to use MRC term as it is own by B+W (or whatever factory actually they come from). Like Hoya filter, they are using HMC, SHMC.