It's basically no different to any cash management account offered by the banks. It's a retail deposit account with Macquarie Bank (not Macquarie Group - MQG) and therefore covered by the Government Guarantee up to $250k. Banks are regulated by APRA and heavily scrutinised.
So the question of safety relates to the Bank, not MGQ. APRA ensures it meets minimum prudential requires for buffer capital. It is credit rated, more information here
https://www.macquarie.com/au/about/investors/debt-investors/credit-ratings/
I would say it's a safe as a cash deposit in any of the big four. But that should not be confused with an absolute guarantee, because there is no such thing.
