Questions about how PS4 region locks work.

I live in Australia, I made a US PSN account and I want to use a download key I can buy here. One of the results in the list of sellers with a Persona 5 key has the US flag next to it. How do I pick the US code over the EU or GB one and will it work with my US account with a PS4 bought and used in Australia.

EDIT: Realized it was not a key, but transferred via account switching. Is this some scam tactic, or is it as easy as the website says it is.

@weeaboodesu: Its a stolen account, stay well away, DO NOT BUY.

If you had asked last week, the AU PSN store was selling it for $50 AUD and the US PSN store was selling it for $40 AUD (after conversion). You really missed out.

@GTR12: Damn, yeah I did miss out. Whatever, my local game shop is having a Christmas sale and it's down to $50 AUD so I'll just buy a hard copy.

Thanks for the help, I haven't bought it from that sketchy site yet so I'm good.