I, for one, am quite pleased with the stainless steel caliper pistons I put in several years ago. My OEM steel ones got pitted and started to leak after a while.
At the same time I also thoroughly flushed the system with silicon brake fluid (DOT 5) and refilled with same. A bit expensive, but necessary, procedure to make the change. Silicon fluid is not cheap. But with its very low moisture absorption, it also seems to protect the aluminum brake and clutch components (wheel, slave and master cylinders) from corrosion. Especially if the car sits for meaningful periods of time as mine has over the years. I vaguely recall hearing that silicon fluid brakes down if your brakes ever get hot enough to boil the fluid. But DOT 5 boils at 550 degrees F. So, at least for non-racing applications, I think it is a better choice than the petroleum based fluids. I do not know anything about the Girling Low Moisture DOT 4 fluid. I also think silicon is kinder to the rubber sealing components in the brake system. Just my humble opinion.
Cheers, Gene