I've been using regular IO for over a year and a half and I always mix up the bag before use. A couple months ago I got a box that mixed up to 17DKH, 680CA and took 2 days to clear up. I complained and they sent out a new box. But this new box mixes up to 6.7DKH and 480CA but at least it clears overnight. So I'm kind of over it, thinking of switching to HW-Marinemix Reefer because it's advertised to be about the same parameters I'm at. I'm using the 17DKH stuff for WCs on some live rock I've got in a brute and to hatch BBS.
I use Brightwell because the parameters on that salt are the parameters I aim for on my tank. Also, always make sure to mix your salt around prior to making SW regardless if it says to or not. Not mixing can affect the consistency of the parameters and potentially ruin a whole box of salt. It's just good practice.