Best on board charger for Kinetik batteries?

There has been a lot of talk about on board chargers lately on the board, and it has been very good information. Here is my specific situation:

I have a pair of KHC 2000 Kinetiks that I will be using for my 'house' system and a KHC 1800 for my starting battery. All Kinetik AGM batteries. I have a perko switch and a Voltage Sensitive Regulator already in the boat.

I sometimes use the boat for a week at a time at Lake Powell, and do not have access to shore power, so simply putting the stereo batts completely separate is not a possibility. I do need the alternator to sometimes recharge them, but would rather have them full every time I go out by charging them at home. It is not that often that I let it sit and play music for more than an hour.

The kinetik guys (of course) would like to sell me one of their on board chargers. They give me some mumbo jumbo about how it is specifically designed for their batteries and it would condition them to run better and last longer. It is pricey, and it only has 1 bank. I don't like the idea much of connecting 2 different battery sizes together on 1 charger, as that they might discharge and charge back and forth and decrease the lifespan. I believe they should be isolated. It also is not waterproof.

The pro mariner sounds great and has a 3 selections for 'Flooded(lead-acid)/STD AGM, GEL & High Performance(HP) AGM'. This is the 'Gen 2" charger. I think the only difference I can find is that the first generation charger has 2 settings for batteries instead of 3.

I am leaning towards the promariner Gen 2 chargers and would put it on the high performance AGM setting. Any thoughts on this or other setups?