In many cases I purposely avoid the center line, and rather have a clear center polygon quads strips. It saves me time and complications in two ways:
When I’m moving points around on one side of the symmetry plane I can pick single points, instead of herding pairs pf points to keep tangency across symmetry plane.
When I have to add centered details (like a button/knob, drain hole) I can do it with booleans/projections to a single converted Nurbs surface, not across seams of multiple surfaces.
I just wanted to add this thought before McNeel starts going in a wrong direction. I have a lot of thoughts on symmetry, after working with SubDs for almost 2 decades now, but I’ll stay quiet for now.
This hacky reflect tool is ok for now until we all have time to make a good solution. There are so many more important foundational things to fix in SubD right now IMO.