You need the Peukert Exponent value based on the brand and model of the battery. A lower number is better. A good AGM will have a low number (slightly more than 1.0).
The bigger issue is your alternator regulator
needs to be set up for AGM too. Screwing up the charging
profiles will really trash an AGM battery fast. Not having the alternator
regulation right to would be costly. The Freedom is fine for shore power charging
even if not perfection. These days AGM's cost too much to screw that up. Done properly the lower internal resistance will allow a faster charge from the alternator. The Freedom is faster too but when docked and plugged in - who cares? The "potential" AGM payout is fewer engine
hours to recharge the battery because the alternator can work at a higher amp rate longer. The low maintenance
is also a bump for you too.
The common problem with AGM is poor charging. They really won't tolerate it.