don't forget lightning enchanted can sub for holy freeze for amp coverage, especially with blood boil which releases the bolts which then proc amp. hf is quite nice, but I wouldn't be opposed wifeswapping my fire enchanted hf cursed spearbae for a lightning enchanted conc cursed version. Even without conc, she still gets the job done.
Its a nice bonus on top of holy freeze but not at all a replacement. Most of the time is spent teleporting around not casting blood boil, and even when you do use blood boil triggering bolts, its often 1-2 extra hits per cast with monsters only on one side of your demon. Whereas holy freeze can be hitting ~10-20 monsters per tick even in fairly sparse areas, for ~40-64% proc per tick, compared to boiling for ~5-10% per cast.
Its important to remember that all the auras are fairly marginal dps bonuses, but amplify damage 200-300% multiplier. If a bound demon already has ~1200% ed from bind/mastery/extra strong/might, adding +270% from conc puts it at +20.7% overall
Proccing amp is critically important to your demon damage output AND your blood boil, so you'd be better off with a cursed + holy freeze + lightning enchanted demon than a demon that had higher DPS but less chance to proc