I have used it for 6 years. It works for me. I started by trying a couple other brands like Coralife and IO and didn't notice any difference then when i switched to MEI Crystal Sea. I have bought mine at hidden reef most of the time. I usually went up there a couple times a year and got 4-6 boxes and then check out the corals. I hope they still have the same price. they sold tons of it every month. It's made just down the road in Baltimore, so shipping costs are much lower than for the other brands.
When i recently started testing for magnesium i found my normal batch mix to be pretty low. maybe because i was mixing to 1.023 SG . i got a reading there of 1150 ppm. and calcium was a little bit low too. but, no problem. i have 50 pound bags of mag flake and calcium chloride for the Randy 3 part system I just do like Randy does and add enough of both to bring the mix up to spec. and i now mix to 1.025 SG which means adding more salt and thus more Mg.
I think it's a good salt and a good value.