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No one knows just how long the LiFePO4s will last since they haven't been out long enough. The testing results I've read about seem to match the manufacturers claims of 2000+ cycles. I'll be too old to worry about them by then
Hopefully some day in the near future they will be cheaper than AGM batteries. My final total cost to convert is about the same as AGM's. This is building the system yourself with individual cells. Which took research and some skill and knowledge. But not more than most people on the forum already have. The biggest problem was putting all of the research together in order to make the charger do what I needed it to.
Basically the best charger would be one that puts out maximum amperage (my batteries could handle 500 amps charge rate without causing damage!) at a maximum voltage of 13.8 to 14.0 voltage, then switches off. If I could find one that would just monitor the voltage then start a charge cycle again at a preset state of charge (SOC) or set voltage rather than float charging. But most chargers want to switch to float which is NOT recommended for these.

UPDATE: The Balmar voltage regulator on my engine worked well. Charge rate was about 150 amps which is very easy on the belts and alternator. We haven't dry camped overnight yet but plan to Tuesday night. I'm anxious to see how the Balmar handles the charging when the batteries are down after overnight.