I no longer have any ,380 pistols, but did extensive work with several some years ago using three or four cast bullets, including a heavy one (a flat nose design of about 120 grains) cast from a SAECO mould. I tried a number of powders, including Herco. 231 was by far the best powder overall as for accuracy, but, nowadays, if I had a quantity of Herco, I'd certainly do some experimenting with it.
I'd have to do some digging into my old notes as I don't recall offhand where I got Herco .380 data. It's possible I may have developed my own so I won't recommend loads. Herco is just slightly slower than Unique, so you shouldn't have problems if you carefully work up loads.
It seems few use Herco these days, but it remains a fine powder worth trying in any cartridge that can be safely used with Unique powder, though load data is certainly not interchangeable. Herco works particularly well for 9mm cast loads.