Bootloader unlockable in all versions?

Hey all, I'm thinking of getting a G2 and wanted to make sure that the newer versions of the bootloader can all be unlocked or downgraded. I found this thread but wasn't sure if it was up to date. I plan to buy on eBay so I have no clue what I'll actually end up with until I have it in my hands.

I didn't do my homework before buying my Galaxy S4 and have been stuck dealing with Samsung's halfassed inefficient and locked down software because of their un-unlockable bootloader for the last year or so. I really want to make sure my phone is actually mine this time.