[notahacker]

You get to honestly veto the candidate you dislike the most (or back the candidate you want if s/he actually makes the final ballot) in the runoff.

But if anything, the first vote becomes even more tactical potentially in bizarre ways such as aiming to ensure that a candidate sure to make the final ballot runs against the most odious fringe candidate on the final ballot.

[bshanks]

Maybe, but I get the impression that overall the addition of a true runoff tends to make things better. For example, this guy compared a number of voting methods using his preferred metric, Bayesian regret; note that when a method and a variant with a runoff added to it are compared, the runoff tends to do slightly better: http://rangevoting.org/StratHonMix.html

In addition, I have no data for this but I expect that a runoff would increase the perception of legitimacy of an electoral result, because while the initial voting procedure that narrows the field to only 2 candidates will occasionally be impacted by counterintuitive results such as spoilers, at least the runoff can always be interpreted in a straightforward manner as "we were choosing between A and B, and most voters preferred A over B".

[lambertsimnel]

> Maybe, but I get the impression that overall the addition of a true runoff tends to make things better. For example, this guy compared a number of voting methods using his preferred metric, Bayesian regret; note that when a method and a variant with a runoff added to it are compared, the runoff tends to do slightly better

I suspect that result is caused by voters being misinformed about how IRV works. It would be interesting to see IRV compared to Exhaustive Ballot, which is like the Two-Round system, but with up to n-1 rounds for n candidates. The last-placed candidate is eliminated each round until there are a majority of votes for one candidate, just like IRV.