The 2015 Spline on Surface can be initially drawn more quickly and with better initial control, but I'm afraid that it is (and will be) forever plagued by the  SW 3D solver (not to be confused with the 2D D-cubed solver.)  For instance, create a simple revolved shape using a conic (like shown below.)  Now create an SOS on it manually spiraling up round it. Now start constraining the beginning and end points - I guarantee you will soon over constrain it. This is an important sketch element that I've wanted to use for a long time - especially since it has the capability to split surfaces but I'm finding that it is no better improved over the previous (<2015) version.

Mark