I use Salifert, but have a SeaChem test kit for Mg. When I needed the Mg test kit, there weren't any Salifert available anywhere.
Here are a few questions ...... what makes a test kit good? Obviously accuracy, but why is Salifert so much better than the others? I like that Habib has lot numbers on all the solutions. What about expiration dates....do all brands have them?
Where do you store your test kits? I keep mine in another room high up in the cabinet (keeping little hands away....no child proof lids), and to have it away from the moisture near the tank. I suppose keeping them in an air tight container would accomplish the same thing.
One comment on accuracy of test kits. IMO, they are only as accurate as the user makes them. For example, if you are reading the wrong portion of the syringe when performing a titration (like in a Calcium or Alk test), then your reading will be off. I believe in the Salifert directions it tells you which part of the plunger to read from. If you consistently perform a test the same way, then you can note general trends, but if you aren't reading the results correctly, then you might be slightly off target.