The main points there are that you need a special "lithium" charger is a bunch of hooey.
A lot of folks will get sucked into forking over hard earned cash to replace a perfectly capable "smart/programmable" charger.
The "standard" charger they are referring to are the lower end RV converter/chargers found in almost ALL RV's. (which are highly inadequate for most battery systems currently in use.. ie., flooded deep cycle wet cells)
The charger you referenced is no different. It's just a plain ol "standard" charger with a higher "factory adjusted" output. It is non programmable. You would be better served to buy a true "smart" charger. Programmable, heat adjusted, and full sensor capability. That would be true with your trojans, AGM's OR LFP's.
They are trying to sell ice to Eskimos.
The "catch" they are trying to scare you with is that all LFP cells charge and discharge at different rates. What they only put in small print is that the cell regulation takes place in the individual cell circuitry.. not within the charger. They DO have different charge requirements to stay happy.. but that's just as true with your wet cells and AGM's.
I understand you are trying to look further down the road, but one other factor you might consider is that you really don't want to be slowly adding cells... mixing old and new cells over a period of years.
It's just my own personal opinion.. but if you have a little extra money right now, you would be better served upgrading the "backbone" (charger, solar controller, battery meter) and sticking with the AGM's. Maybe go with 4-6v'rs and give yourself 220ah's on tap (440ah @ 50% discharge).
In 5 years.. once the LFP's are more reasonable in price... and you've gotten your dollars worth out of your AGM's.. THEN make the jump to LFP.
I know there are folks that are able to take advantage of LFP's now.. but typically those folks are running high voltage 24v or 48v system powerhouses. Probably somewhere in the 1% range of typical RV solar setup's... and there is still not much debate over the fact that the $ to Ah is highly unbalanced. Some of those folks are heavy boondockers that NEED that kind of power storage to run their self levers and hydraulics that might over tax a small 12v low power system.