Hiya! The specs on this wiring kit seem a little 'optimistic' to me. Ampacity (maximum safe current) for 8 gauge wire is typically considered to be 55 Amps. Your 750 Watt inverter, assuming 80% efficiency, probably draws almost 80 Amps when running full-out.
There are charts for this just a quick Google away, but here are a few good ones:
How-to-Size-Wiring-and-Cabling
Voltage_Drop_Chart
5-Percent-Voltage_Drop
What you'll see is that, at these currents, the length of the wire matters (shorter is better). If you're only running 5 feet of wire, you can use this kit and be happy. (But 5 feet of wire only puts your inverter 2.5 feet away from the battery -- your circuit is a loop.) Any further, and you need to step up to 6 gauge or 4 gauge.