shunt.
I am not familiar with this particular guage, but generally, ammeters that require no shunt route all of the load current through the gauge itself. If that is the case, I would opt out. It would mean lots of fat wire, and the load being routed behind the panel. The purpose of the shunt is to provide a remote means to sense current loads. This is a MUCH safer installation, and has the capacity to save a good deal of weight. Also, high current loads traversing the panel is bound to wreak havoc with sensitive radio and nav equipment. I would get more information about this gauge before you decide.
Regards,
Chris