Tx,
The lugs must be listed for more than one conductor. I agree with your concern.
The TVSS works better when its leads are as short as possible / practical and when they are connected as close as possible / practical to the lowest impedance conductors in the assembly.
I've attended a couple presentations by a local power quality consulting group that cleary demonstrates the benefits of not just slapping the TVSS unit in to "get it hooked up". The best TVSS performance is achieved by reconfiguring the existing hardware enough to provide lugs as close to the main service conductors as practical, and to mount the TVSS unit to keep the leads short.
