If you read the description, you get 2-4 trays, and each tray fits 2 gearlocs worth of dice, so you have capacity for up to 8 gearloc dice sets.
I'm assuming they give you trays based on your order, so base game only comes with 2. If you added on 3 characters, you would get all 4.
Ha, fair enough - I'd read the sentence:
We love this design as it allows you to pull out your removable trays, toss them across the table to fellow Gearloc players and it becomes a part of the game area (stores their skill dice close to them until they unlock them and place them on their character mat).
...and assumed 1 tray per Gearloc.
But you are quite right, higher up it notes that each tray stores enough for two Gearlocs. I suspect they'll give all four trays to each backer - that would be one tray per Gearloc for base backers (which fulfils the above awesome vision) whilst providing storage for "gotta have 'em all" backers like myself !