Does the $400 upgrade process instantly? Or does it just buy you a "chance" at an upgrade?

UA has offered a product like this for years now (or at least PMUA did, I'm not sure if it's still around or not), but your upgrade did not actually confirm until the gate, where I presume you were put into queue based on status alongside people upgrading using miles, etc. Which still sucks for the person who might otherwise have gotten a free op-up, but at least does not cost anyone the use of their SWUs. Not clear if this is what Delta is doing or not.