Sure, I actually understand this now, and there's been a lot of back and forth over this issue lately, so here's how it is.
Originally Posted by alxn
Each level, you unlock a WEAPON ATTACHMENT TOKEN, and weapons, skins or equipment. At given milestones these are EITHER OR decisions, which lead to us building unique personas, and not all migrating to the same loadouts.
There are 50 levels. Each class is independent, for levelling purposes, this means you get 50 attachment unlocks for each class, and then you get to build a second class at the end of it differently.