most important thing is to get a 4 pole switch, this allows you to kill everything if needed. and that kit wont work as you need about 16-20 ft of positive cable
What you want is a 4 TERMINAL switch, which is "two pole"
A 2 terminal switch is "single pole"
You can take the second set of contacts, ground one terminal, run the other forward and hook to one end of a relay coil. Use your switched ignition to trigger the other end of the relay, and use the relay contacts to either kill ignition, or to kill the alternator field.
If you have a "one wire" alternator, use a relay as above to kill ignition, or a heavy relay/ solenoid to kill the alternator output.