Australia uses it both for House and Senate elections. Millions of votes cast in a day. Indicative count on the night.
My tone is dismissive because I am tired of being told IRV is "too complex" or "won't work". Because it's simple and it has scaled flawlessly for decades. You just need to believe the experience of other countries is more valid than a theory.
The AU senate is STV, no? And even then, the largest polity is NSW with only 8M people. 12 US states are more populous than this.
But, I'm with you that IRV is workable (there's ample evidence) and better than the abomination that FPTP is. I guess my point is that AV/SV address these concerns through their simplicity (I find both of them less complex than IRV in both voter UX and result computation) and also that they avoid the unintuitive problems mentioned in the OP ncase link, which can potentially be even worse than the problems of FPTP simply because they are hard for even educated voters to wrap their heads around, whereas the problems of FPTP (vote splitting) are easier to explain (but still bad. this isn't a defense of fptp).
My tone is dismissive because I am tired of being told IRV is "too complex" or "won't work". Because it's simple and it has scaled flawlessly for decades. You just need to believe the experience of other countries is more valid than a theory.