Might want to read the C-Store page a little more carefully... some items are for all characters on an account, some might be one per character unlocks.
For example, you'll note that costume packs have "Note: Purchase of this option unlocks these costumes for every Federation character on an account." attached to them, meaning you only need to buy it once and it will unlock for all your characters on an account.
Edit: Original post was incorrect. You can claim the Tribble on all your characters. The fact that it says "Buy Now" on the features page is a bug. Fortunately, you can't actually buy it, and if you go to the Special Unlocks tab, you can claim it on all your characters after its been purchased.
Last I heard, the expected functionality of the Tribble C-Store item is that it needs to be purchased individually for each character. I apologize for any confusion this may have caused. I will let the team know that the UI is not completely clear about this.
Thanks Destra, I must say, I find that quite surprising.