I would agree with this statement if it was restricted to systems that are only connected to LFP. If the charge is going through a combiner that is connected to AGM start and LFP house, if the LFP shuts down, the AGM is still taking the charge so no harm, no foul.
That's true.
Consider, however, Yandina's installation manual for their combiners:
"A better solution, in our opinion, is to connect the alternator
output to the house battery bank by connecting it to the load side
of the house battery switch. When the house bank rises to 13.1 V DC,
the Battery Combiner will close and allow the engine starting battery
to charge in parallel. "
Start banks are almost always full because it only takes a few ah to start an engine, even with glow plugs. Most of us, except the neanderthals in the UK, route the AO to the house bank, so the combiner is only moving current to the start bank AFTER the house bank's voltage rises enough to close the relay, meaning the house bank has had an opportunity to get some charge and is not depleted as much as when charging just begins.
Now consider an LP house bank with a relatively much smaller AGM or wet cell start bank. While the start bank's chemistry will absorb an LP shutoff of the AO, the combiner is now being tasked with carrying far higher currents, and, as such, the wiring between the combiner and the banks must be carefully sized to so accommodate this increased amperage. Yandina's manual suggests wire sizing that would lead me to believe they consider only AO>>house bank>>combiner>>start bank. The amperage going the other way, especially with LP that can absorb a lot higher charging currents than wet cells, should be considered when sizing this wire compared to Yandina's
"Use 3’ (minimum) of 6 AWG wire to connect the contactor on the Battery Combiner to the positive connection point of the electrical system.
Use 4 AWG wire for the 200 amp model. Do not use shorter lengths of
wire; the tiny amount of resistance is helpful to reduce the maximum
current."
Just something for installers to know about.
EDIT: written before I saw Maine Sail's excellent solution.