I've never used the RSCP salt but I've been using salinity for a long time now and I love it. Of all the salts i've used, salinity requires the least amount of salt to get to my desired 1.026 level. I've used multiple buckets and have not had to adjust my dosers either.
Yeah salinity is more expensive, but IMO ur using less salt to Mix sw so the price is comparable to other salts u use that are cheaper and require more salt.