You get people on the Westwood side of EK that use the 6 to town. The 6 is the only route fron EK that goes through the Southside too , 31 does is suppose.
Yeah the 21 from Westwood to town would be significantly longer as the section up to Calderwood is a bit long winded. Quite like the 31 tbh except the part through Kirktonholme and Stewartfield. Feels pretty long winded but from Philipshill to the city centre it's really good compared to the 6