I don't have any experience with the Magnum AGS specifically, but have been using auto gen start for close to 20 years now. I love it, but there is one think you need to watch out for, particularly on a boat.
You need to be sure to stop and start the gen with no load on it. Otherwise you risk burning out the voltage regulator.
If the Magnum inverter is the ONLY load, then you are all set since it will wait for the gen to start before it applies it's load, and drop the load as soon as it sees the gen falter, or before it commands a shutdown.
But on a boat there are typically other loads that do not go through the inverter like a water heater, other chargers, etc. Those loads will have to be manually turned on and off, or just left off when using the auto start. If you want to get fancy, you could automate switching of those other loads, but that's probably more complicated that you want.