what is the difference between the various types of magnesium?

The following website will explain the differences: https://www.globalhealingcenter.com/natural-health/types-of-magnesium/

Does this product have any salicylates or quercetin from its original source?

While we do not test for salicylates, the only potential salicylate-containing ingredient in the magnesium glycinate would be a small amount of corn from the ascorbyl palmitate. The amount of salicylates would be negligible.

Does this powder have any taste once mixed with water?

This product is absolutely NOT "tasteless" as described. It tastes like a mild form of milk of magnesia, especially after I added a sweetener (honey) to the water to try to make it more palatable.