Milton Friedman was not part of the Austrian School. Rather, he was part of the Chicago School. While both schools promote free market economics, there are differences. In fact, one of the biggest differences has to do with their views on central banking, with the Austrian School generally being against fractional-reserve currencies while the Chicago School being more sympathetic. Milton Friedman was a monetarist.

Milton Friedman also rejected one of the central Austrian tenets, the business cycle.

Friedman was a Chicago monetarist, not just an Austrian hack. Pure monetarism doesn't always work, as it ignores irrational behavior, but it's not _useless_. Monetary models work great in steady-state conditions for fine-tuning and in cases where the monetary supply results in high inflation.

The 2008 economic crisis demonstrated that brilliantly. The IS-LM model correctly predicted the outcome of fiscal expansion (lack of inflation, despite trillions in stimulus) and the futility of monetary measures (negative rates in Europe did not result in economic growth).

As someone else said Friedman wasn’t an Austrian. Not even close. The only real similarity is that they both are proponents of free market capitalism. Friedman was a mainstream economist who used mathematical modeling and statistical methods. The majority of Austrians don’t use either and prefer reasoning about individual actions from first principles.