Some things I have noted thus far (only been using for 1 week - but have had to do some massive water changes lately for a nitrate issue):
Salt is far more concentrated and does take longer to mix
You can actually smell the potassium in the mix (and it does have a distinct "chemical" like smell do to being more concentrated - SeaChem has actually confirmed this and states that there is nothing to worry about)
Salt mixes better if you warm the water slighting before adding the mix
What I like is that every batch is lab tested and numbered so if you do have any issues and actually think you have a bad batch, SeaChem can confirm if you do or not. (which is nice because I was using Brightwell's and noted a lot of inconsistencies from one bucket to the next)
I love the bucket it comes in, LOL (seriously though, it's a really cool bucket)
In one week, three (or four, don't remember) water changes later, my coral color has come back in my LPS to be much more florescent, specially the orange and greens, my Ca and Alk have leveled out far better than with Brightwell's Salt mix, the polyps are coming out more on my SPS and my LPS is more open/puffy (Lobo is like twice the size, Trachyphyllia is much more puffy and has also doubled in size, Hammer and Torch are both looking much healthier in both color and extension of tentacles - they're fatter, instead of looking really stringy and unhealthy, I hope someone knows what I mean by that, and both the Blastomussa Merletti and Wellsi have never looked better since I first bought them.
I honestly did not believe my LFS when they said, "You'll notice changes instantly," but honestly, I really have. I would never have expected a change in the corals in less than a months time.
I know some one you will go, "but wait, didn't you say you had a nitrate issue?" Yes, I did, but we're using this salt in more than one tank, tanks that did not have the nitrate issue also were switched to this salt and the coral in them has improved just as much.