@zenogias First, mesh symmetrize works great as long as you have your mesh positioned correctly along the local origin. You may be thinking of the Topology Mirroring. Sometimes referred to as X symmetry. Mirror modifier is definingly better in my opinion. Second, This post is about Armatures, which don’t have modifiers. It’s X-Axis mirror can be buggy too, but the Symmetrize option under armature/right click context menu work great as long as you have the bones named correctly and positioned properly along the local Y axis.
