Brazilian living in Ireland here. The system used in Brazil doesn't help with weeding out extremists (as it's painfully obvious right now). Ranked voting, OTOH, heavily punishes rejection, which results in reducing the size of the Overton Window in politics.

The two dominant parties here are both center-right and are barely distinguishable to the point the Green Party formed a government with them. This is undesirable if you want quick changes, but exceedingly good if the aim is long-term multi-generational stability.

It does help, but not much. It basically enforces that the most rejected candidate does not win. But it does nothing to the second most rejected one.

Of course, ranked and approval voting are much better choices.

We have a similar system for electing the Mayor of Richmond, Virginia. It's biggest drawback is that the 2nd election is needlessly expensive, and since it's out-of-cycle and there are no other elections occurring at the same time turnout is much lower. I would prefer instant runoff.

I don't know about the costs, but here in Brazil the turnout for the second round isn't much lower: for instance, for the 2018 federal elections, the turnout was 79.67% in the first round, and 78.70% in the second round (source: official results website). But that's probably because voting is mandatory (except for voters younger than 18 years or older than 70 years).

This can be really bad if the vote is split enough that the top two candidates are not the actual voters' preferred top two.