Lhf definitely not always the best option. It seems to be a fixed rate so it's more useful for luxury, one way and/or busy dates when normal prices are high. Otherwise yeah, persistent checking and testing code combinations can beat it. My next two rentals, lax 3 day and tpa- mco 13 day, both cheaper for full size (after regular checking) using Costco 7014627 and one of the codes I posted above.
The Tpa-mco one for full size went from $520 to $211 just by repeated checking so that's always a good idea. Lhf was in between at $320. But for luxury same booking best price Costco and dollars off coupon, $746. Luxury via Lhf code and dollars off, $467.