I've always used Instant Ocean, or Reef Crystals as I mentioned.
Here's the deal with saltmix in my opinion, based soley on my limited experience with this hobby.
The saltmix I choose, and we're all free to choose whatever we want, is only one part of the puzzle.
It's no guarentee for success, nor is it going to doom me to failure.
It's a saltmix, and how and what I mix it with can and will determine how it tests out.
I've been able to get IO to test out at different levels for pH, calcium, alkalinity, ammonia, nitrate and phosphate - just by mixing it with different freshwater sources, and varying the aeration time of the "freshwater" vs the "mixed saltwater".
Once we mix up a batch of any saltwater and add it to our tanks - there are so many other factors that can affect the health of the tank, that I've never focused too much on the brand.
I see my choice of using a particular brand of saltmix as just another choice in the hobby.
To me .... it's how I mix it, how I use it, how I run and maintain my tank that is the real challange.
There are so many manufacturers of saltmix, all seem to have their followers, all seem to stay in business.
I can't imagine if a saltmix was so bad that it caused people to fail at keeping a marine tank running well .... that the company would ever sell another bag of the stuff.
I still think it's a personal preference, one that each person will make for his or her tank - according to their own experiences.