Bumping this because I'm wondering the same thing. I put the cart in front of the horse a bit and got a good deal (i.e. budget) on a new-fangled LFP house battery to complement my FLA start batteries before doing anything with my charging system. Now I'm faced with possibly converting my Hitachi 60 amp alternator for external regulation, and then using some mix of Orion dc-dc charger and/or an argofet along with all the related fuses and cabling. It all adds up.
Maine Sail's "Drop-In LiFePO4 Batteries" article at MarineHowTo depicts the Balmar APM in both the argofet and Orion scenarios. Of course I'm inclined to accept the general wisdom of this, but if I can get away, at least in the short term, with not having to buy an APM in addition to everything else, then I might be inclined to put it on the back-burner. In the event of a BMS disconnect, wouldn't the FLA absorb the full 40 amps or whatever my diminutive alternator might be pushing out? Likewise with the Orion?