I found out that GALLAYWAG'S LOCKER WILL NOT give you an extra Vault if you already have 28 vaults (sorry gang no 29th vault). so because it becomes soulbound upon Assembly DO NOT redeem it on a character that already has the maximum number (28) of vaults
For the record, do not redeem OR assemble it on a character that can not make use of it.
The four parts of a calendar reward can be traded to other characters on your account. Once the parts are assembled, the assembled item becomes soul-bound.
Indeed, you can collect them all, use shared vault or mail to give them to any of your alternate characters (or save for later use if you only have one) but it is correct, that this gift will not create a 29th vault page.