The conversion between hertz and rad/s or deg/s does not produce the expected results.
Example 1: 360 deg/s gets converted to 2pi Hertz

Example 2: 2pi rad/s gets converted to 2*pi Hertz

The expected result for both of these conversions is 1 Hertz (https://en.wikipedia.org/wiki/Radian_per_second). I would expect the quantities package to either produce 1 Hertz or to throw an error due to incompatible units.

I suspect this is because radians are dimensionless and so they can convert from rad/s (dimensionless/sec quantity) to hertz (1/sec quantity).

The core of the issue is that "Hertz" as a unit is defined as 1 cycle per second, but is commonly used for angular velocity with 1 cycle = 2*pi radians implied.

I'm not sure of the right way to fix this but one option would be to define a new quantity of "angularHertz" defined as 2*pi rad/s, and throw an error if the plain-old hertz is converted to/from an angular velocity.