I concur. Did this on a old 2007 Subaru with a PO420 code many years ago.. Still passes inspection to this day. I don't believe the cat was actually shot.. maybe something more along the lines of the exhaust leak.... letting in oxygen into the exhaust stream.. thus throwing the po420 code.
Make sure exhaust is tightly sealed... If it really is the cat.,,. look for the CA emission version, yeah it cost a lot more... but you will not be replacing it in 13 months.
EDIT: What's up with the low voltage btw? I would fix the volt issue... maybe the o2 sensor is not getting enough volts to read correctly? Im just throwing out ideas.