Perhaps not certain, and I do agree that there's far more to be gained by replacing plurality voting by either, but I think that page has some mistakes.
> IRV leads to stifling 2-party domination
I suspect that's because of poor voter information. You can't address every political problem effectively with a choice of voting system.
> with IRV, that one round is more complicated and it cannot be done on ordinary "dumb totalizing" voting machines
> IRV is more complicated for both voters and talliers.
I find IRV simpler as a voter because of the reduced need for tactical voting in the first round.
IRV isn't complicated to count by hand. (In my country, vested interests said we couldn't afford the necessary voting machines, but we already conduct hand counts suitable for IRV.) You simply separate the ballot papers by candidate and count each candidate's vote, as we do under plurality voting. If no candidate has a majority, eliminate the last candidate, redistribute that candidate's votes to the highest ranked candidate (as marked on each ballot paper) still in the race, count only the redistributed votes and add them to the total from the previous round. Keep going until a candidate has a majority.
> we certainly cannot argue that one system is better than the other under all circumstances.
You have to choose an electoral system before you can know the exact circumstances of an election, but the he main thing is to avoid plurality voting.