One other caution about using FLA or some of the vehicular lead-acid chargers, is that some will assume that low-voltage batteries are sulfated, and will start to zap them with 16v "desulfation" pulses to try and force them to accept a charge, which obviously are bad for LFP.
Ie, if you have a very discharged LFP below about 10.7v, the standard fla-charger may start shooting those desulfation pulses out.
So be careful out there if using one of these...