I used to buy it. Then I bought an RO/DI and started making my own with IO.
I don't know if it's worth the extra money it costs. I also noticed that the SG was always about 1.019.
Never could figure out why it had less SG than NSW.
Some day, I'd love to pull water right out of the ocean; but, with everything I read, I've been too chicken to try it on a tank with critters I really care about.
Best of luck,
Roy