Not sure. i use regular IO for emergency WC as it has lower ALK as well.
Salts for NON doser people who wish to keep a SPS tank would be IORC RSCP
SALTS for EMERGENCY WC for lower ALK SPS tanks like i prefer might be FRITZ RPM, IO, RED SEA regular bucket "NOT CP". Julian sprung TWO LITTLE FISHES "Acurasea " Which i do like actually, nice stuff, lower ALK and natural levels is there selling point.
I can't speak for other salts as I have not tested them. But I do know some folks worry about FRITZ possibly using "cheap MAG" and not storing well. I have no issues to report and use it in 48 hours at most. usually in 6 hours.
Reef crystals mixing horribly common issue. I hear fosters smith "live aquaria /divers den" have a similar salt to FRITZ but never tried it. I hear Tropic Marin is awesome stuff don't know which salts have what levels. and no interest in probiotic enhanced salts. heard things enough said.
Severlal other brands I have little or no experience in to make judgements.
I think it matters if you make RO or RODI. I think it matters what the temp it is at. I think it matters if you properly aerate the RoDI first then add salt. Matters to add salt to super highly stirred water slowly can't over mix the water while adding like 2000 GPH + stir pump. I have tried things like boosting PH a bit with KALK before I add salt n so forth, with no real worth while results.
Things like all that can effect how a companies salt mixes. I also try not to store saltwater too long as i have seen RSCP drop ALK big time in a month if stored in a sealed unstirred BARREL for example in use with a AUTO water change system. I came back and i don't even wanna say what the levels are in the barrel at 30+ days but it was real bad and I stopped doing that immediately and learned alot about Salt mix and whats in my mix when i make it up from that time on.
My main reason for any salt mix is it is affordable, clean, consistent, and makes what matches parameters my system. Many folks test ALK and other parameters, before they do the Water change. Which is good advise, unless you can afford a mistake.
Hot salt is a whole new thing now as well thats supposed to be interesting. Can't speak about it. I'm not educated on it. New way of making SW MIX supposedly.