I see a number of problems with the methodology (eg. excluding data points after an arbitrary one-week-after-study-midpoint which author acknowledges as arbitrary, doing an averaging/smoothing of results per location first, then doing a global calculation, which compounds the error).
But the numbers do seem reasonable. Still, the difference with flu is that there is no protective vaccine to give to people at higher risk, nor do we know exactly what constitutes the higher risk, nor do we understand exactly how transmissions happen or why they do not happen.
Also note that we are already in a largely manipulated situation to be able to judge any "organic" data (we've been social distancing, hugely reduced international travel, and a stronger dedication to doing business online). While some will point at the number of people still behaving normally, I always point at the number of people who are not, reminding that this is a "game of statistics".
Finally, to me personally, global IFR and R0 numbers do not matter. I do not care how many people are affected, but how much risk does the infection pose to my close family and friends and me? It seems there is a strong correlation between heart-related diseases and coronavirus deaths, so I would like to see numbers for "extra coronavirus deaths over heart-related deaths" for an "unmanaged" first month in the US (eg. April had ~60k people, May-July another 90k). My parents, both with heart problems, barely made it through flu season a number of years back (they've been on flu vaccines since). Heart-related deaths in US average out at 600k/year or 50k/month (did not find per month averages to account for seasonal spikes). To be honest, I expect to see a huge decrease in heart-related deaths in these months, but I couldn't find anyone doing a study along those lines (or well, simply having access to current numbers)! Still, none of that helps me until there is (safe! still a year away likely) medicine to prevent or treat COVID19.