Although I have not personally observed the breakin phenomena occuring with AC conditioners, I've been told by both a manufacturer & an "authority" (one of their dealers) that breakin does in fact occur with their devices. I've certainly experienced breakin improvements with interconnects & speaker cables, but I haven't noticed this happening in my rig with line conditioners, or even AC cords for that matter. I'm not saying definitively that it does / does not happen; just haven't had the pleasure at my house, but as always YMMV.