The biggest disadvantage is it creates horse-trading and "how to vote" cards. The largest two parties will do deals with all the minor parties to try to gather

The biggest disadvantage is it creates horse-trading and "how to vote" cards. The largest two parties will do deals with all the minor parties to try to gather their second preferences on their "How to vote for us" cards and mail-out advertising. And then independent candidates don't just have to be #1, they have to beat the major parties PLUS all the other independents who traded their second preference advice to the main parties... That ends up being why the "two-party preferred" polls (which of the two main parties are you going to rank highest) end up being far more important than the primary vote (who will you pick as your #1 preference) in Australian opinion polling. So it is a nice idea, and I do like that Australia has it, but for single-winner elections (rather than the Aussie senate where six candidates get elected from each state-wide vote), it perhaps makes it harder not easier for independents to win.