I seem to remember a discussion of the various salts in the Reef Chemistry forum, including tests of the various salts, just a few weeks ago. A quick browse should turn that up.
A bunch of reefers use Instant Ocean and IO Reef Crystals, many for many years. It has performed well for many of us, and there don't seem to be any significant considerations for not using it.
As far as storing it outside in a brute can, I would not recommend that, as the Brute trashcan isn't airtight, so humidity would be likely to get inside. The salt would absorb the humidity and likely cake, or in extreme conditions you could end up with a barrel of brine.