I've been using NeoMarine for some time now. I really like it. Mixes quickly if you bring your RODI up to temp before starting the process. It has a sulfur smell at first but is normal and will be gone by the time it's clear but something to consider if you mix in living spaces. The parameters are very close to what I keep and have been consistent for me.
I'll say I only mix what I plan to use now. If I do that within a day or two everything is spot on. I feel the alk does drop over time. I'm a little more strict on testing before water changes now so I'm not sure if that's something specific to this salt mix or that I just started to test before wc. Previously I always mixed 55g and used as needed, keeping it heated and mixing.
If you've never bought it before, buy the bucket not the box. The bucket has a great seal on it and is needed, that salt is so dry it will suck up moisture like crazy. If you buy the box, it just comes in a ziptied bag and I'd imagine it will absorb moisture and harden quickly. I buy boxes now, but have multiple clean buckets from previous purchases.
I'd recommend neomarine over blue bucket. I've used both. Neo Marine is lab grade with samples kept back with awesome CS. If you have a serious issue, they have the ability to test your batch number. Red sea I believe is harvested and dried, it also leaves a film/residue in my experience. When mixed properly NeoMarine leaves very little residue, similar to TM at a cheaper price point.