I've been using it for about 10 years now. I mix mine with bulk Epson Salts from San Francisco Salt per Randy's instructions. I also use Dow Flake for Ca and soda ash from a swimming pool supply for alk. I've never had any chemistry issues. On my old 425g system I did very, very few water changes over 5+ years... but that system had a 180g (8'x2'x16") sump/fuge/DSB/frag tank. Oh, and I never had any fish issues either. The only problems I ever had were aiptasia, majano anemones and flat worms and none of those were related to my chemistry.
I live in SW Florida and I had friends visit from up north and bring me mag and Dow Flake when I needed it. Obviously we don't melt much snow in SW Florida. Then I found a tennis supply house that sold both locally here in Florida! What a shock! They use it to keep down dust on clay tennis courts!